Argument 2: Gay marriage is wrong because homosexuality is wrong

That's an opinion, which is neither shared by all faith groups, nor supported scientifically or medically. You are entitled to disagree, but not force your disagreement into policy against the preponderance of evidence.

Homosexuality is a normal, natural variant in animals generally (not limited to primates). I like to use the analogy of left-handedness. This occurs even in the most right-handed of families, around 10% of the time and in all populations and cultures. It is an inconvenience, at most. But historically (and in some cultures still today) left-handedness is viewed as satanic (hence the meaning of "sinister" which is Latin for "left"), and a sign of error. Even into the mid-20th c. in America, lefties were forced to "be" right-handed--to be "normal"-- often at great cost --until we realized there was nothing wrong with some people being left-handed. Hmmm, sound familiar?

So, if it's a normal variant, what's to be afraid of? Any more than we are afraid of red-heads or lefties. Homosexuality persists at a low level throughout human populations. It isn't 100% correlated with genetics--almost nothing in human behavior is. On the other hand, the evidence is convincing there is a genetic component. People generally do not choose their orientation, although sexuality is a very fluid concept. And remember, nearly all gay people grew up in straight families.

Please spare us the "it's not the orientation, but the act". The "love the sinner, hate the sin" thing is offensive to those of us who understand that being gay is not a pathology and not a "sin". Most of us as humans want to be loved and have meaningful, complete relationships with the one we love. And no, that's not a justification for promiscuity: it's a plea for marriage.

One thing about gay marriage is, it promotes the same values for gays as it does for straights. Faithfully partnered gay couples raise kids, support their families, contribute to their communities. Our sexuality may not be "appealing" to the majority of straights, but here's a hint: straight sex is just as revolting to most gays.