ok... first of all... marriage is a religious institution, but not of christianity. the pagans, woulds, and germanic tribes of europe were doing it way, WAY before christianity came about. so were various tribes and religions all over the world. many of them weren't polygomous, so don't start with no gay or bi marriages.
second of all, you cannot choose to be gay. you do not turn gay later in life, you realize it. it's a mutation in the genes. if you don't believe me, try to turn yourself gay. honestly, if you think you can turn yourself gay and then back, you shouldn't be afraid. turn yourself gay. sexually want someone of the same gender. it isn't easy, is it? neither is forcing your genetic structure to follow society's standards just because christians said so.
in the end, religion doesn't decide the laws of our country. morals and needs do. basic human morals are being kind to your fellow man, not banning the ability to love another man. it's religious morals. don't force religion on people, don't force sexuality on people. gays have never done anything like that to you.
actually i'd like to see an example of gays ganging up on straight people because they're straight, or trying to pass laws based on their sexuality. apparently a lot of people thing gays need to leave straights alone. why can't they stand to leave gay marriage alone?