Christianity is often held up as a reason to take various political positions in this country, in part because it emboldens the "pros" by believing God is on their side, and in part because it makes the "cons" take the uncomfortable position of criticizing God. After all, if God opposes stem cell research, then who are you to question that, Professor McSciency?
The problem with this of course is that the Bible--the operating manual for Christianity--leaves a lot of room for interpretation. Reading the Old and New Testament, it's very hard to imagine they're both talking about the same God. I can sum up the OT--God creates mankind, mankind keeps pissing off God, God keeps punishing mankind. At some point he made the Israelites the Chosen People, gave them specific rules to follow--more on that in a bit--and ordered them to slaughter anyone in their way (He helped out from time to time with that). Then in the New Testament, God sent his Son to save mankind by letting mankind brutally murder him for no good reason. The Son was also God, which is why there's not two Gods, though it seems in the NT that they're two different beings so it's not entirely clear how that works. Before getting murdered and resurrecting, the Son taught mankind a lot about love and forgiveness and charity and peace.
Now, the OT did in fact have a lot of strict laws--laws about not eating certain animals, or wearing certain types of clothing, or leaving your hair uncovered, for example. One of these laws, importantly for today's political debate, is a strict ban on homosexual acts--calling them "abominations" which is pretty severe. In the context of all of the OT rules about sex, though, it's pretty clear why the "gay ban" is in there--the Israelites were a small desert tribe surrounded by enemies and following a religion at the time that did not take in converts. It was quite likely that the tribe was one unfortunate battle or bad plague away from being wiped out completely, so the rules God needs to come up with would favor requiring that the only sexual activity be used for procreation. Multiplying is crucial in that sense. This explains why even heterosexual sodomy is forbidden, and widows who could still bear children were encouraged to re-marry. It also explains the food laws--many pork and shellfish products at the time were unsafe and God wouldn't want his tribe dying out from that. So it sort of follows that man laying with man or woman laying with woman would decrease the procreation activity.
Of course, Jesus in the NT doesn't mention homosexual activity, and does in fact tell His followers that they wouldn't have to follow most of the old laws (which is why Christians today don't keep kosher and aren't required to get circumcisions or get bar mitzvahs). And this makes sense--Christianity is a religion all about converts, and far greater numbers to work with. It also follows that Christianity would not require any stance on homosexuality--although the one most consistent with Christ would be one of understanding.
That said, if someone wants to oppose homosexuality--considering it "wrong" or "unnatural", whether an innate tendency or simply a lifestyle choice like drug use--they're free to make their arguments. But they should really leave Christianity out of it.