Why does gay marriage matter to those who have nothing to do with it? "Getting mad at someone else's marriage because it's against your religion is like getting mad at someone for eating a doughnut because you're on a diet", a very true statement. Why does it matter those who don't have to deal with it? The radical christian and Muslim cultures that condemn gay marriage don't understand what it is so they immediately believe it's wrong. People are scared of what they don't understand.
There is the argument of emotion and there is that of law and logic. The colonists came to what is now the United States in order to escape persecution from the state they had been oppressed by. So why don't we see that we are doing the same to them? We persecute them for being different in a land that was founded on being different, and believing different. There should be a separation of church and state as well, why should the Bible define marriage? What of those who aren't Christian and don't follow the Bible? Why must they be forced to follow a text they don't believe in?
People need to be more tolerant of other walks of life, tolerance is not understanding something, accepting something, but to see that you don't understand but not condemn them for being different.