Two consenting adults want a civil marriage? Seems reasonable enough to me, and I haven't yet heard a good argument against it. This civil union stuff (ie: separate but equal) is shameful. Let them in on civil marriage, hope that it leads to more stable relationships in that community, and continue about your business being largely unaffected by them. Or even better, get the government out of the marriage business all together and let the issue become moot.
The argument that this will lead to human/animal marriages? Well, really Rip, even you aren't that stupid.
And the argument that churches will be forced to perform ceremonies and accept homosexuals into their congregations? Ask your local female Catholic priest about how Affirmative Action has helped them get ordained by the church, or your nearest homosexual Mormon who was able to force himself/herself into a local congregation with the help of anti-discrimination laws. Good luck in your search. Fortunately, religions are pretty well protected in our society against outside interference beyond causing harm to those unable to fend for themselves.
And and the argument that why not let more than two people get married if we're going to let the gays get married? Well, why not? Certainly doesn't bother me if some bozo wants to burden himself with multiple nagging wives. Really sounds like a self-induced hell-on-earth though, but hey, different strokes...