Ok, so let me get this right. You fear that gay people will feel normal about who they are, if we give them marriage rights. Funnily enough you illustrate my arguments beautifully, because that's the crux of it - what gay people do isn't wrong - it's their choice on how they live their life. Everyone should be able to live their lives according to their own beliefs, and considering Christianity doesn't own marriage, but is now a secular union, I don't see why a gay couple cannot use this to mark their relationship in the way society has done with other normal relationships.
Regarding Christian marriage, well there are plenty of ministers who are keen to perform this role so that won't be an issue.
On the point about other religions, yep I agree - there is little in history regarding same sex marriage, even in tolerant societies. Not sure exactly why that matters though, we don't live in those ages and we have come a long way and evolved our thinking to a greater degree. As such now is a perfect time to create a world which operates better than those that have been before.
