The problem with voting against gay marriage because the Bible tells us it's a sin - and why religion shouldn't guide our laws.

I've had this debate with a very christian (not catholic) friend of mine. She has gay friends and doesn't have a personal vendetta or problem with them at all, but, if asked to vote on the right for gays to marry she would absolutely vote against it. The reason is because according to the bible this is a sin, she feels like she cannot condone it. Now for someone who genuinely is anti gay because of his/her religion, I somewhat get the logic. But for someone who's got no other issues with gays other than the fact they're described as sinful in the bible calls for a wider perspective. For me, voting against gay marriage is basically FORCING people to adhere to your views. Gay marriage doesn't force you to marry a gay person, and some gays are very entitled to not get married if they believe it goes against their religion. Gay marriage has no influence on your ability to live by your religious code, but voting against it influences those who do not.

And to put this in perspective, I would call on christians here to think of it the other way around. I'm an anti theist, meaning that I would actively debate against religion and seek a secular society. BUT, this does not mean I want to force you to be an atheist. As such, I would ALWAYS defend rights to have a religion. I would NEVER vote on a law that forbids people from being religious or have religious buildings to gather. Laws are not a matter of fitting with my opinion, they are a matter of defining the best ways to live together, in diversity and respectfully. When religion guides the decision that we should not allow people to marry, or have an abortion etc., we are directly imposing our views on them although we have no right to do so.

So the question then for me is, as christians what is your perspective on this, and if you agree how would you phrase it to my friend?