I think it is safe to say that in almost every culture throughout history (until recently), recognition of same-sex unions has been extremely rare. Specifically, in Israel 2000+ years ago, almost everyone would have had a hard time wrapping their head around how that was even possible. It is possible to say with certainty that there were absolutely no notable efforts to create legal structures for same sex unions.
For people who condemn homosexuality on religious grounds, it is a secondary question whether or not there is historical precedent for gay marriage/unions. Or how marriage has been traditionally defined. At the core of the matter, what really sells the case is the argument that the Bible classifies any homosexual behavior as sinful.
In ancient times, when gay marriage was essentially non-issue, it would have made no sense for the Bible to support or condemn it, or even to mention it. So it doesn't. Similar to how the Bible does not take a stance on stem cell research, because that issue did not exist when it was written, and any attempts to discuss it would have just confused people.
But although the Bible does not take a stance on homosexual relationships, it does take a stance on homosexual behavior, and the question is which ones. If the message is that all homosexual behavior is sinful, then the implications for homosexual relationships can easily be worked out. On the other hand, if only certain categories of homosexual acts are considered sinful, such as temple rites and rape, then it leaves the door open to acceptance of gay marriage.
To be honest, I don't know enough about Greek, Hebrew, ancient Jewish culture, or textual analysis to get a firm grasp on the answer, although I'm leaning towards thinking that the more permissive explanation is correct. I'm guessing, though, that some of you are much more studied on this issue than I am. What do you think -- does the Bible condemn all homosexual acts, or just a nasty subset of them?
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