what that means is that if the religious psychotics want to define marriage as heterosexual, i actually think they have a right to do that, as marriage is their idea and their institution. a secular society rooted in atheist civil traditions would not have marriage at all, as it is not a secular idea and doesn't make any sense in a truly atheist worldview.
it would follow that if gay people want to invent their own religion and define their own institutions, they ought to be free to that, i guess. i mean, to the extent that any kind of marriage is stupid, gay people getting married isn't any more stupid. this isn't something the state should be involved in defining or overseeing, it ought to be a religious institution and process that the state has no power to interfere in.
this is a legal and civil opinion: marriage is obsolete, but gay people shouldn't be told they can't get married, if they can find a religion to marry them, and they really insist.
but, my personal opinion is that gay marriage is a dumb idea that is attempting to enforce a concept of human nature that is contrary to our biological instincts and our normal behaviour. lesbian marriage strikes me as particularly stupid. nobody should be surprised to find out that gay marriages rarely last more than a year, and the average length of a lesbian marriage is measured in months. these girls are all just lying to themselves.
when i meet married lesbians (particularly), i have a hard time taking them seriously. either they're (in fact imminently) going to cheat on each other and end their friendship in a vicious cat fight as they accuse each other of being controlling, or it's an open relationship and they're not really married. this is not real marriage by any sort of meaningful definition, and no thinking person would ever interpret it that way.