Celibacy and contradiction with modern medical science

Because you added hyperlinks to specific references as I requested let me try to analyze them. I wish you'd quoted specific sentences from those references, but let's try to summarize the whole documents.

Enlightenment through Celibacy or Celibacy through Enlightenment? doesn't mention masturbation at all, except in the Vinaya which are the rules for nuns:

In the bhikkhuni Vinaya there seem to be several rules to safeguard against sexual practices such as masturbation, h*m*sexuality etc. The restrictions in the Vinaya againstsharing the same bed, couch, sharing the same blanket, from rubbing each others bodies, applying oils etc on another could be multi purpose including to safeguard against possible sexual activity.

The later sentence which says, "The above clearly shows that abstinence from sexual activity is not the essence of the practice towards Enlightenment even in the case of a monk or a nun" means I think that it's not the activity that's wrong, it's the self-indulging in a desire for a (conditioned) sense-object.

Are you asking about the Vinaya rules for monks, or asking about the "five precepts" rules for laypeople?

Its conclusion includes,

Having examined the lives of disciples above it is difficult to conclude that celibacy is a pre-condition for Enlightenment. ... . With progress on the Path, realizing the true nature of sensual pleasures and the mind and body one progresses through to a celibate life naturally. Some reach such a state of mind earlier than others . In any event at the latest, with the attainment of third fruit of the Path, Anagami-phala one switches over to complete celibacy. Ajahn Brahmavamso writes; ⋯ since sensual desire has been totally transcended, there is no spark left to ignite the passion for sex. All Arahants are ‘potently impotent’.

Note that Anagami-phala isn't being free of sexuality in particular: it's being free of "sensual desire" or Kāma-rāga in general.

Most of this document describes rules about bhikkhus. These Vinaya rules don't apply to laypeople (whereas in contrast these are some suggestions for laypeople).

You quoted Wikipedia's Buddhism and science article in your opening sentence which claims that "Buddhism ... insists on revoking everything that could not be proved by scientific method or rational thought".

Wikipedia's article says several things, none of which justify your assertion that "Buddhism insists on revoking everything etc."

This is discussed in many other topics on this site, which you can find by searching for words like "faith", "belief", and "kalama".

You reference Masturbation: Questions and Answers for your claim that "masturbation is a healthy way to relieve sexual desire or tension".

I read its "Health Benefits" section as saying:

• It lets you practice or become more skillful at sex
• It lets you practice sex without a partner

I don't suppose that Buddhism contradicts those statements, and maybe there's therefore no "contradiction with modern medical science."

What Buddhism might disagree with is whether "practising sex" and "becoming more skillful as sex" are desirable: whether that's Buddha's message about the four noble truths.

In summary, if there's a conflict between Buddhism and masturbation, I think that's because Buddhism:

• Teaches that learning freedom from sensual craving is "better" than pursuing sensual craving
• Teaches that there are other ways (other than sexual activity) to "alleviate stress"
• Does NOT believe that (unlike eating, for example) sex is necessary, that sex does not lead to the creation of new feelings, and is therefore a component of the Middle Way

I will quote/extract a few sentences from Wikipedia's article on that subject, below (you can read the whole article and its references for further details):

An article from Beliefnet and Brian Schell, a writer for DailyBuddhism.com, both suggest that masturbation is essentially harmless for a layperson, at least outside the realm of karma[3][4] The accomplished Theravadin monk Bhante Shravasti Dhammika cites the Vinaya Pitaka in his online Guide to Buddhism A to Z, stating the following

Some people during the Buddha’s time believed that masturbation could have a therapeutic effect on the mind and the body (Vin. III, 109), although the Buddha disagreed with this. According to the Vinaya, it is an offence of some seriousness for monks or nuns to mast**bate (Vin. III, 111) although the Buddha gave no guidance on this matter to lay people. However, Buddhism could agree with contemporary medical opinion that masturbation is a normal expression of the sexual drive and is physically and psychologically harmless, as long as it does not become a preoccupation or a substitute for ordinary sexual relations. Guilt and self-disgust about masturbating is certainly more harmful than masturbation itself.

The emphasis on chastity in Buddhism is much more so for bhikkus and bhikkunis (monks and nuns, respectively), who are expected to follow the Vinaya (traditional code of ethics for Buddhist monks and nuns). Not only are monastics celibate, but they also must strive to conquer their desires much more so than a layperson.

Thus, in Buddhism, masturbation and its permissiveness is most often viewed as situational, depending on one's level of precepts and monastic standing.

The "Buddhist stress on celibacy" which you refer to is (arguably) 'stressed' for monks and nuns; and it is not stressed in exactly the same way for laypeople.

Some of the other Vinaya rules too (e.g. not eating after noon), which are only applicable to monks and nuns, might or might not not be perfectly in line with every recommendation of "modern medical science", but apparently they are good enough for their purpose, which I think is to 'allow the holy life to be lived'.

Also, science and Buddhism don't contradict each other on this subject, they say different things about it:

• Science suggests that masturbation might have some effect on the incidence of some types of physical illness.

• Perhaps Buddhism doesn't say much on that subject (see "Buddha gave no guidance on this matter to lay people" above), but if anything IMO it suggests that masturbation might have some other effects (e.g. on discipline, views about desire, profitable use of time, etc.).