http://pagesoffaith.wordpress.com/2012/12/02/perspective-on-homosexuals/ , which was then translated into Hebrew, which one major Israeli news website then rather hilariously translated back into English).
The argument goes like this: both the Talmud (Chullin 92a-b) and Midrash (Genesis Rabba 26:5) openly decry gay marriage--the former cites banning it as one of the few things non-Jews do right, while the latter blames Noah's flood on allowing it.
Really? Let's look at the first source: "Ulla said, 'These are the thirty commandments which the sons of Noah accepted upon themselves, but they only fulfill three: a) they do not write a ketuba for men; b) they do not weight dead meat in the market; c) they respect the Torah.'"
What is a ketuba? Essentially, it is a prenuptial agreement, designed to protect widowed or divorced women from being left destitute. The text does not make clear whether we are talking about two men marrying each other or men in general who are marrying women. Yes, Rashi takes the first approach, but he himself does not conclude whether the "dead meat" referred to in b) is of human or animal origin. Moreover, this is presented among the things which humanity (the sons of Noah) "accepted upon themselves," not those which they were commanded by God. Finally, this passage appears in the Jerusalem Talmud (AZ 2:1) in the name of an earlier sage, but without the three exceptions.
What about the Midrash? "Rabbi Huna said in the name of Rabbi [Judah the Prince]: 'The generation of the Flood was not washed away until they wrote hymenaios for buggery and bestiality.'" Hymen, of course, was the ancient Greek god of marriage, and hymenaios is a genre of lyric poetry and song in his honor. One can imagine what kind of songs these might be. Yes, there are some who translate this term as "ketuba", but the etymology does not support it, not to mention the ridiculous image of writing a prenuptial for a sheep! If making lewd jokes about gay sex brings a Deluge, there are more than a few yeshivot which might want to look into flood insurance.
The relationship of Judaism with homosexuality is a fraught one, but we do ourselves no favors by reading our texts casually and peremptorily.