[I]t's only when gay people bring up a passage like Deuteronomy 22:20-21 that you hear anyone say, "Oh, that stuff about stoning daughters to death on their wedding nights if they're not virgins is in the Old Testament, you goof! That's not in the New Testament!" If it's out-of-bounds—totally not kosher—for gay people to bring up what the Old Testament says about clams and farming and personal grooming and tattoos and menstruation and virginity and adultery, then it shouldn't be kosher for conservative Christians to bring up Leviticus and Sodom & Gomorrah. Which they do. Constantly. And it's not like they have to: there are, courtesy of Paul, plenty of anti-gay verses in the New Testament. But those verses aren't anywhere near as hateful or murderous as what you'll find in Leviticus, of course, which is why they're nowhere near as popular with anti-gay bigots who call themselves Christians.
And, of course, the story of Sodom and Gommorrah has nothing to do with homosexuality but with being unwelcome to strangers.