The only possible way for religious people to respect the sanctity of their marriages, would be to ban government sanctioned marriage, period. Civil unions for all! A contract between two people that determines legal rights/responsibilities related to government.
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Marriage should be completely unrelated, because who the fuck decided that the "sanctity" of your marriage is determined by a fucking government employee? The government isn't your god, and it doesn't give a fuck about your love. Don't be fuckin' stupid.
If you want to legally tie yourself to another person you trust, I don't care who you are, as long as you're willing to accept the consequences alongside the benefits. But if you just love someone and wanna marry them? True sanctity would mean that you just go and do it freely.
Go to a church if that's your thing. If they won't marry you because they're hateful pricks? Fuck 'em. Find one that will. And if church *isn't* your thing? Go into nature with your friends and family and just do it. All that should matter is that you love each other and say you're married.
Bottom line...anyone who's against gay marriage doesn't actually give a fuck about the sanctity of marriage, because if they did, they wouldn't let the fuckin' government have anything to do with it in the first place. All they care about is hating gay people and keeping them down.
Because if you're *going* to say that marriage is a governmental act, and if you're going to tie property rights, medical rights, financial rights, etc. to the "legality" of a marriage? As long as a man and woman who aren't even in love are allowed to do it, there is no basis for restricting it.