A rabbinic interpretive tradition (one which goes back at least to the fourth century C.E. and is found in the midrashic book Sifra) understands another verse in Leviticus 18 to mean that the locals in Canaan actually conducted same-sex marriages, among other forbidden sexual practices the Canaanite peoples had sanctioned. It was for this that God ejected them from the holy land: "Do not become contaminated through any of these [acts]; for through all of these the nations that I expel before you became contaminated. The land became contaminated and I recalled its iniquity upon it; and the land disgorged it inhabitants" (vv. 24-25). The Canaanites suffered national defeat, invasion, humiliation. Finally, they disappeared from history. (Did you ever meet a "Canaanite"?)

The Bible doesn't frown on gay sex uniquely. In the first five books of the Bible (the Torah), homosexual intercourse isn't the only act called an "abomination." The book of Deuteronomy applies the terms to certain unethical business practices, which in Leviticus are denounced as a "perversion" (see Deut. 25:16, Lev. 19:35).

But same-sex intimacy is unique (along with incest and sex with animals) in being pointed to as among the failings of a non-Jewish people, the Canaanites, that brought about that group's final moral dissolution. I don't know of another category of sin that, in the biblical context, is both a) explicitly made applicable to gentiles and b) is spoken of in such emphatic terms as leading to societal breakdown, whether the society in question is Jewish or not.

Basic moral principles apply not only to Jews, in other words, but to all people, even those that don't follow Jewish dietary laws. If any country defies them, it will suffer a fate akin to the Canaanites'. The men and women of Canaan were not held responsible for not observing the Jewish Sabbath--to pick another example of a practice asked only of Jews; but they were held responsible for rejecting the fundamental moral tenet that marriage is between a man and a woman.