Why is gay marriage such a big issue?

If ity is believed to be a sin that causes eternal suffering, what about all the rest of the sins? According to the Bible, each and every sin you commit proves that you're infinitely imperfect in the eyes of the Lord. Lying and lusting would get you screwed as much as being gay would, by that logic. So why is uality condemned so much more than anything else? If everyone sins anyway, then there's no reason, IMO, for people keeping a strict interpretation of the Bible to crack down on ity any more than any other things.