Wanting to redefine marriage is a liberal goal, not libertarian.
I agree marriage is a religious institution that has no place in government. That being said I just made up a religion called wookie-ism. According to my religion, gay marriage is great and straight marriage is horrendously appaling. I am running for office and am hoping to outlaw straight marriage, as the wookie-ists hate it.
You obviously don't understand libertarian thought. Mind your own business, who cares if gay people marry, it has NO effect on you or anyone else whatsoever. If you think they are going to hell, good for you, why don't we outlaw premarital sex too? Gay sex? Oral sex?
I'm not an anarchists, I believe in 2 criminal laws, which the government should enforce.. don't hurt anyone else physically, don't take what isn't yours. There you go, that is my entire criminal code. The jury/judge system is generally intelligent enough to appropriately decide punishments if you break one of these laws.