Separation of church and state doesn't mean separation of common sense. Until the last decade or so homosexuality was deemed wrong pretty much worldwide by nearly every religion on the planet. It ain't just Christianity. In fact I don't know what type of Christian you could claim considering the religious text that guides you pretty much deems homosexual acts one of the worse sins possible.

Religion happens to deems homosexuality wrong. Along with murder, bestiality, stealing, etc. Religion didn't "make" homosexuality wrong. It would be wrong even if there were no religion. It's just an easy argument to blame it on religion because to try to make sense out of it on its own merits would be impossible.