An interesting question. I'm not sure if I can give you a completely honest answer, due to cognitive bias. But I will try. Let me preface and say that, in college, I used to advocate the whole "love who you want, marry who you want, it doesn't affect me" mentality. It doesn't "hurt anyone else." That sort of thing. Of course now, I cannot ever go back to that. That was primarily out of indifference; I didn't actually CARE because the issue didn't actually affect me. But it seemed "fair," in my worldly view -- how is it fair I can love and marry and someone cannot, since they love and want to marry someone I wouldn't? It seems hypocritical, if you will, from the worldly perspective.
My honest answer, in your hypothetical situation, is I likely would revert to a state of lack of caring, as before: so it's a yes and a no. I wouldn't "oppose" it, because I wouldn't care about it. Since I'm not gay, the issue doesn't affect me, so I'd probably be on the fence due to indifference. Most say they care -- however, it's my experience, they don't REALLY care; it just seems more fair, from the worldly perspective. Besides, live and let live is non-confrontational, despite more-than-whom-will-admit it's against nature and in general, an off-putting topic overall. Alas, my morals at that time in my life seemed more modern than such an ancient book written by plain old humans.
I can empathize with the position, believe me.