Let? This seems to be a big misunderstanding amongst humans - the idea that rights are given to us by some higher authority. Nuh-uh, existence grants our rights. The best our entitled humans may do is refrain from removing them by threat of force. Have a nice day =D
The right to marry has lots of legal implications which are controlled by the state, and marriage is controlled by the state, and has been for millennia. If you think it's not, you're deluded. Common law marriage does not really exist, legally.
Now, should it be controlled by the state and have lots of legal implications? That's a different question. I personally don't think it should, but trying to remove marriage from the legislature would be quite difficult.
The point is that for quite a while now homosexuals have had the right to live as couples, but they've not been allowed to be recognised under the law that gives tax breaks and other things to married couples. I'd personally do away with these tax breaks and make marriage a purely personal thing, not something legal (but as I said before, this will be difficult).
Until that time, I'm perfectly happy with homosexuals marrying on the same basis heterosexuals do.