Why do many who believe that “all are born sinful” hold that “none are born gay or trans”?

I can only speak from a UK context, where there isn't a Christian right like there is in the US. But I think the way the church has handled issues of sexuality is similar. In the last 10-20 years, the church here has come a long way in understanding sexuality. Organisations such as Living Out have been set up within the past few years, helping people to put the pieces of the Bible together.

Unfortunately, I think many in previous years held to traditional Christian ethical beliefs without really holding to other fundamental Christian beliefs (e.g. total depravity) - the morality became divorced from the theology. What you ended up with was a kind of Pharisaism where sexual sin such as this was seen as particularly bad. It was much more common in the mid-20th century to see h*m*sexuality as something that was chosen, and many church leaders have simply inherited this view without thinking through how it fits with theology.

This is why, for example, in Tim Keller's review of Matthew Vines' book, he says:

And when I see people discarding their older beliefs that h*m*sexuality is sinful after engaging with loving, wise, gay people, I’m inclined to agree that those earlier views were likely defective. In fact, they must have been essentially a form of bigotry. [My emphasis] They could not have been based on theological or ethical principles, or on an understanding of historical biblical teaching. They must have been grounded instead on a stereotype of gay people as worse sinners than others (which is itself a shallow theology of sin.) So I say good riddance to bigotry. However, the reality of bigotry cannot itself prove that the Bible never forbids h*m*sexuality. We have to look to the text to determine that.

I think this is what has happened over the past 10-20 years. Many organisations and churches who own the name "Christian" have been shown that, although they may claim to hold to views such as total depravity, do not think it through when it comes to issues of morality.

I should add that I think this is a sensitive and complex area because different people have different views. For example, in the UK, the Core Issues Trust do not describe what they do as conversion therapy, but they believe that it is sometimes possible for someone to undergo change in their attraction. And having a strong view of sin (e.g. total depravity) I don't think is totally incompatible with believing that aspects of our desires, including sexuality, are a choice. But I don't think that's exactly what you were asking!

There is no contradiction, once you base your argument on doctrine of the origin of sin in man. Unlike Catholicism and its original sin, which is the sin that every human being is born with after the fall, because of Adam's sin. In other words, it is a sin contracted by us not committed, but still you are born a sinner.

Catechism of the Catholic Church; Section Two: I. The creeds; Chapter One I Believe In God The Father; Paragraph 7. The fall

403 Following St. Paul, the Church has always taught that the overwhelming misery which oppresses men and their inclination towards evil and death cannot be understood apart from their connection with Adam's sin and the fact that he has transmitted to us a sin with which we are all born afflicted, a sin which is the "death of the soul".291 Because of this certainty of faith, the Church baptizes for the remission of sins even tiny infants who have not committed personal sin.292

419 "We therefore hold, with the Council of Trent, that original sin is transmitted with human nature, "by propagation, not by imitation" and that it is. . . 'proper to each'" (Paul VI, CPG # 16).

Protestants do not believe that you are born a sinner, but the concept of original sin is that which Adam committed, causing the fall. From which we are all born with a fallen nature, a corrupted and sinful nature. We are born sinful.

Westminster Confession of Faith; Chapter 6, Paragraph 2

By this sin they fell from their original righteousness, and communion with God, and so became dead in sin, and wholly defiled in all the faculties and parts of soul and body.

London confession of faith 1689; Chapter 6, Paragraph 2

Our first parents, by this sin, fell from their original righteousness and communion with God, and we in them whereby death came upon all: all becoming dead in sin, and wholly defiled in all the faculties and parts of soul and body.

And it is for this reason that we are unable to do good (seek God, or fulfill his commandments; Romans 3: 10,11) and inclined to only do evil (follow the designs of our flesh, of our heart, wherever it lead us; Galatians 5: 19-21)

So according to this doctrine, you cannot be born gay or trans or adulterous or p**nographic or liar or murderer or greedy, etc, but you are born with a biased nature to do any of these things to get away from God. And it is only through Jesus Christ that we are freed from the slavery of sin. But until the restoration comes, we will continue to struggle with these sins as well as Paul in Romans 7: 14-25, but we must maintain a life that mortify those sins Colossians 3: 1-17

Your statement on Calvinism’s Total Depravity is not correct. The two main beliefs are Calvinism and Arminianism. John Calvin was based on the foundation laid by Augustine and John Wesley on the foundation laid by Arminius.

Both believe in original sin, but Catholicism believes also in shared guilt in Adams sin. Some, mostly Calvinist Protestants ascribe to this as well.

Calvinism teaches Total Depravity like this: Human beings are so affected by the negative consequences of original sin that they are incapable of being righteous, and are always and unchangeably sinful; human freedom is totally enslaved by sin so we can only choose evil.

Arminianism teaches: Deprivation – Human beings are sinful and without God, incapable (deprived) on their own of being righteous; however, they are not irredeemably sinful and can be transformed by God’s grace; God’s prevenient grace restores to humanity the freedom of will.

So both beliefs teach original sin but in very different ways.

However even Catholics teach original sin and this is a driver in infant baptism in that all are seen as sinners, even babies before they consciously sin.

Many churches believe however that God provides power to overcome sin and this includes the various forms of h*m*sexuality. Reformed (Calvinist) churches are less likely to subscribe to this believing we are incapable of ever not sinning.

Arminianism faiths are more likely to subscribe to the belief that Gods power is transforming, and thereby conversion is possible.

Gender, the image of God, and biology

People who say that "I am born gay" are implicitly saying that their gender is rooted within their most fundamental constitution of being a person, namely at the level of what Christians call being made in the "image of God". Since at this level it is correct to say that they cannot change who they are, they then claim that they cannot and should not change their gender, that their gender takes priority even over the biological expression of their gender, manifested in the morphology of their sexual organs. It makes sense, then, that some of them attempt to "fix" their sexual organs to align with what they think as their "immaterial gender" embedded in their personhood.

But many Christians say that God himself determines a person's gender at this most fundamental level, taking the cue from Gen 1:26-27:

²⁶ Then God said, “Let us make human beings in our image, to be like us. They will reign over the fish in the sea, the birds in the sky, the livestock, all the wild animals on the earth, and the small animals that scurry along the ground.”

²⁷ So God created human beings in his own image. In the image of God he created them; male and female he created them.

Those same Christians hold that:

• this predetermined gender is embodied biologically at birth as a God-given reliable sign of this gender. Quote from a blog article by Preston Sprinkle (theology professor with PhD in New Testament, author of the 2021 book Embodied: Transgender Identities, the Church, and What the Bible Has to Say) from Part 7—Male and Female in the Image of God of his blog series on Sex, Gender, and Transgender Experiences:

  We’ve discussed three pieces of evidence for this claim: (1) one’s self declaration, (2) the brain sex theory, and (3) the sexed-soul theory. I’ve interacted with some of the salient pros and cons of these views in previous posts. In short, I’ve found all of them to be insufficient defenses of the claim that a biological male, for instance, might actually be a woman from a theological anthropological perspective.

  ...

  1. The body is essential to our image-bearing status

  Not every theologian has agreed with this. Throughout history, many theologians, in fact, said that it’s our rational capacities as humans mark us out as image bearers. But in the last 100 years or so, virtually every Old Testament scholar (and now most theologians) has recognized that an “immaterial” understanding of the image of God goes against the grain of the original context of Genesis 1.[ii]

  ...

  In short, the biblical usage of “image” (selem) and the ancient background of this concept show that humanity’s embodied nature, and not just their immaterial spirit, or soul, or rationality, is an essential part of how we bear God’s image.

  2. Male and female is correlated with bearing God’s image

  We do not just image God as embodied humans, but as sexed humans. Notice that Genesis 1:27 connects “male and female” with the previous references to “the image of God” and “his own image.” That is, our male and female sexed bodies (images) are in some way correlated with our status as image of God bearers. ...

  ...

  Genesis 1:27 is one of the most powerful, provocative, and, one might say, progressive statements in all of Scripture. Not only are all males (not just kings) said to bear God’s image, but all females as well. The radicality of this truth is intrinsically connected to both our human embodiment and more specifically our sexed embodiment. If sex differentiation is irrelevant here, then the profound elevation of females as distinct from males loses all its power.

• studies that try to find biological explanation for sexual orientation in DNA or brain are inconclusive. Quote from a 2018 Answers in Genesis article Are Some People Born Gay?:

  Both past and present scientific studies have shown no conclusive evidence that h*m*sexual behavior is biological; and even if there is a biological basis, the researchers themselves admit that it would likely make a relatively small contribution (less than one-third if at all, with the environment and other cultural factors having a much greater influence).

• we can instead explain sexual orientation at the more malleable psychological layer, the layer which is affected by nurture. Quote from a web article Is Anyone Born Gay? by Christopher Yuan who wrote the 2018 book Holy Sexuality and the Gospel: Sex, Desire, and Relationships Shaped by God's Grand Story and who earlier wrote a 2011 memoir about his journey from same sex attraction to deepening relationship with God:

  The American Psychiatric Association made this statement as recently as 2015: “Some people believe that sexual orientation is innate and fixed; however, sexual orientation develops across a person’s lifetime.” Scientists are far from discovering the factors that contribute to the development of sexual attractions, so it’s untenable and irresponsible to claim that the innateness of sexual attractions is a proven reality.

SUMMARY: Christians believe that when God creates our individual soul He pronounces it good. It makes sense, then, that those Christians believe that the biological embodiment of the our gender is also good and should be the standard for one's gender self-declaration as well as the guide for one's psychological maturing of sexual orientation.

Original sin, image of God, and restoration

But does original sin affects the gender of a person at birth? This is basically your question. The answer is NO, explained below.

First, let's clarify some terms. Original sin has to do with our inclination to sin, influencing our moral behavior to the point that Paul calls us enslaved by the power of sin. A subset of those who believe in original sin also believe in total depravity, meaning that we are utterly powerless to overcome this, needing to rely 100% on God's grace. But despite the pervasiveness of the depravity, it is extremely important to understand that total depravity does not annihilate the image of God (see R.C. Sproul's answer Does the doctrine of total depravity teach that we have lost the image of God?)

Returning back to the group of Christians referred to in your OP, they believe the following:

1. Gender is predetermined by God, part of a person's "image of God" which is either male or female.

2. Total depravity doesn't compromise this "image of God" in a person; rather there is this power of sin at work which enslaves us at the moral level (our inclination), not at the anthropological level (our being). Therefore, the biological embodiment of our "image of God" is still good, untainted by total depravity.

3. To use an informal language, it makes sense then that they don't agree that a person can be "born gay". Rather, they will say that a person is "born enslaved with the power of sin" which can affect one's sexual orientation development very deeply but not deep enough to affect the bedrock layer of the "image of God" within a person.

4. They, as well as sufferers like Christopher Yuan, don't see same sex attraction in itself as sinful, but as a challenge to win over just like how other people are battling other manifestations of the power of sin such as propensity to anger, laziness, drunkenness, etc.

5. There is hope though, once a person is born again:

   • Even though we started with the condition of total depravity God would not let us be tempted beyond what we can bear.
   • The grace of God helps us to overcome the power of sin and through the sanctification process the effect of total depravity should be lessened. Grace of God has the potential to restore our sexual orientation to what God has chosen to give us at conception. In this way, the original goodness of our sexually determined "image of God" within us can shine brightly as God originally intended.