Marriage between people of different ethnicity was banned in various places well into the 20th century. Both religion and science were used to justify these bans, just as they are used to justify opposition to gay marriage. I'd like to say that I hope opposition to gay marriage becomes as unacceptable as opposition to interracial marriage, but I've just found a report that last year a Kentucky church banned interracial couples from attending services there.

Not all churches, or all church members are against gay marriage, which raises an interesting point. Akenaton says God is against gay marriage, other Christians say he isn't - how do we know who's got it right?