Thou shalt not lie with mankind, as with womankind: it is abomination. Lev 18:22
Among the interpretations of this Leviticus verse, one is the most obvious while being a bit esoteric: it as the prohibition against two men sharing a bed, for whatever reason, or even sharing the room where they sleep. Naturally, one of the Talmudic sages (R. Judah) interpreted it in this particular way, whereas the others strongly objected. Because they did, this law is kind of optional, and so the acceptance or rejection of this law can be considered as an indicator of general attitudes. Interestingly, the medieval rabbis en mass rejected this law because, as they argued, sodomy was unheard of in their congregation for many centuries. Only around 1600 this law came back:
...The incidence of sodomy among Jews is interestingly reflected in the Halakhah on mishkav zakhur (the Talmudic term for homosexuality). The Mishnah teaches that R. Judah forbade two bachelors from sleeping under the same blanket, for fear that this would lead to temptation (Kiddushin 4:14). However, the Sages permitted it (ibid.) because homosexuality was so rare among Jews that such preventive legislation was considered unnecessary (Kiddushin 82a). This latter view is codified as Halakhah by Maimonides (Yad, Issurei Bi'ah 22:2). Some 400 years later R. Joseph Caro , who did not codify the law against sodomy proper, nevertheless cautioned against being alone with another male because of the lewdness prevalent "in our times" (Even ha-Ezer 24). About a hundred years later, R. Joel Sirkes reverted to the original ruling, and suspended the prohibition because such obscene acts were unheard of amongst Polish Jewry (Bayit Hadash to Tur, Even ha-Ezer 24). Indeed, a distinguished contemporary of R. Joseph Caro, R. Solomon Luria, went even further and declared homosexuality so very rare that, if one refrains from sharing a blanket with another male as a special act of piety, one is guilty of self-righteous pride or religious snobbism (for the above and additional authorities, see Ozar ha-Posekim, IX, 236-238).
http://www.jonahweb.org/sections.php?secId=90 On all evidence, this law was on its way of becoming obsolete, like the law of stoning the stubborn and rebellious son (Deuteronomy 21: 18-21): the sages argued that THERE NEVER WAS A REBELLIOUS SON, NOR WILL THERE EVER BE -- and that was the end of the issue. The same ruling was applied to the leprous house and the condemned city. Why was it written in the Torah, if it is impossibility? -- So that people might study it, and receive reward for their efforts.
http://home.earthlink.net/~ecorebbe/id18.html Keeping men separated was impractical in European medieval household, and the only justification for following this extreme precaution (given the uncertain status of the prohibition) was the actual incidence of the transgression it was supposed to preclude. The latter was simply unheard of through the medieval period, to the degree that some rabbis were complaining that they do not understand (!) what the Torah and the Talmud are talking about; then, centuries later, it picked up again. That happened more-or-less when the Jewry left the ghetto.
The rabbis had no incentive for under-reporting the vice in their communities. How is then this "medieval anomaly" explained within the view that homosexuality is "natural"? Within this view, the only explanation seems to be that the medieval Jewry was purged off such inclination, which makes it interesting from the standpoint of genetics.
It is the kind of fact that poorly fits into any of the current explanations ("naturalness", "social construct," repression, etc.) In Christendom and the Islamic world, the diatribes against the vice were commonplace through the entire medieval period, despite all the repression; nothing worked. It was as effectual as it is today. And yet...