As a Christian, I do believe that the Bible teaches that homosexuality is a sin. However, I don't know if sin should be illegal, or if I should vote in accordance with making sin illegal, because we are all sinners and would obviously all be in jail if the government followed God's law.
So it's a complicated issue for me. On one side, I think homosexuality is immoral, but on the other side, I don't know if the government should (or can) follow God's law. I can't think of any Biblical teaching on how a government ought to be run, and my political views are very underdeveloped, so I am undecided as to where I stand.