Not really sure how to vote in the poll, but I don't really believe it's possible for a "Christian" to oppose gay marriage. Such hatred and bigotry makes a mockery of everything Jesus ever stood for.
I always chuckle when non-practising folks and liberal prots make sweeping declarations about who is and isn't Christian.
I'm even less qualified religiously to comment on this as an atheist. That said, to me the real question there is whether homophobia or the belief that homosexuality is immoral is a part of modern Christianity.
I think most people would say that the Hebrew bible and New testament are allegorical documents, at least in large part. They express certain negative sentiments towards gayness, sure. But, you need to put those statements in the context of their time. Back in Bible times, having a gay son could mess up your family's continued livelihood in terms of land title and child labor. Plus, people just didn't understand why people were gay and didn't know that gay people are born that way. Many people thought infectious disease was also a moral issue back then, that disease was a punishment from God. We know better now, just like we know better that homophobia is wrong.
So, just like Christians don't keep kosher or follow the cultural and religious laws of ancient Israel, they don't necessarily need to view homosexuality as wrong.