What are the differences between sex cults and the tantric tradition?

Seduction is the undertaking of Maras.

Remember when daughters of Mara were trying to seduce the Buddha?

That's evil.

When beings first start having sex this occurs;

Those who saw them having sex pelted them with dirt, ashes, or cow-dung, saying, ‘Get lost, filth! Get lost, filth! How on earth can one being do that to another?’

Lust comes into play due to perversion of view, seeing attractiveness in the unattractive;

Perceiving constancy in the inconstant, pleasure in the stressful, self in what's not-self, attractiveness in the unattractive, beings, destroyed by wrong-view, go mad, out of their minds. Bound to Mara's yoke, from the yoke they find no rest. Beings go on to the wandering-on, leading to birth & death.

Therefore;

Sexual intercourse is to be abandoned. With regard to sexual intercourse, the Buddha declares the cutting off of the bridge."

I think it is clear that there can be no Buddhist sex cults, only sex cults.

According to the dictionary, the term 'cult' doesn't necessarily pertains to something negative or false. The cult can be healthy and original. A group of wise men can take texts of tantric sex and relive the original powerful practices of established tantric traditions. In fact, tantric traditions can become old and no longer living (more ritualistic rather than conscious, scientific, intelligent).

On the other hand, cults can be bogus while tantric traditions hold the original teachings and practices that bring people to enlightenment.

First, a cult in the proper sense is simply a group of people who follow the practices of a single teacher. Cults are not inherently bad, and in fact most established faiths are technically cults to the extent that they follow the singular teachings of someone like Gautama Buddha, Jesus Christ, Moses, Muhammad, etc. However, cults can at times form around poisonous leaders who present themselves as wise or enlightened. One must suspend disbelief in matters of faith, but one should not abandon it entirely...

Tantra in the modern (lay) sense is a system generally holds that sexual energy can be used as a tool in spiritual development. Technically speaking, tantra is any system that tries to weave esoteric teachings and practices into common, everyday life (not separate out esoteric life into monastic settings), but because of the emotional power of sexuality in everyday life, tantra has gradually been subsumed by sexuality in the Western world. At any rate, tantrics take sex far more seriously than most people, and it's rare that you'll find a (proper) Tantric teacher who indulges in sex with disciples, acolytes, or lay practitioners. Sex is not 'casual' for them, and their goal is not sex in itself but the ecstatic state that one can achieve by the cultured flow of sexual energy.

Of course in the Buddhist sense, sex is a dangerous fixation. Most Buddhists on the high (monastic) path renounce sex because it is too subject to tanhā. The monastic life becomes a world distinct from the ordinary world, in which higher states of being are cultivated. Tantric traditions have survived in Tibetan Buddhism, primarily in deity and energy yogas. Tibetan Buddhists accept sexual practices as well, though not without consequences (see the recent troubles in the Shambhala Movement). Most modern sexual Tantra derives from Indian/Hindu traditions, which have always carried a more congenial (if complicated) relationship to sexuality (through Shiva/Shakti deity practices). But in the West, with the West's typically prudish-prurient attitudes towards sex, poisonous teachers are rife. One needs to take care.

There is a HUGE difference between Tantra sex and sex cults. Tantric sex is for one purpose only. That is that the union of two people becomes a microcosm of union with the universe, a state of enlightenment. The entire motivation is love and compassion And desire for enlightenment to serve all. There is no lust. Sex cults thrive on lust. Orgasm is for personal pleasure. There is a power differential. There are innumerable religious leaders who purportedly were encouraging sex between themselves and students. That is very wrong. It is not tantric sex. That is abuse of power.