A "marriage" in what sense? To what degree does the state have ANY interest in marriage? Its authority is strictly secular, so any recognition of the relationship between two people would be limited to purely practical, legal matters. No discrimination exists between two people -- of whatever combination of genders -- who want to form a legal relationship -- the concern of the state. So the state has reached it boundary in the matter.
Marriage also has (and is arguably defined by) its religious/spiritual dimension. That is beyond the scope of state power. If two queers can find some worthless "church" that will "marry" them, fine. But just as the state has no power to regulate religion on homos, so homos have no right to regulate religion. The state cannot enforce recognition of homosexual "bonds" as marriage, except in the secular, purely practical sense.
It's also worth noting that marriage as an institution was far more stable before the state was ever involved in it. In fact, today a marriage is the one legal contract that is broken with such boring regularity that there is are entire branches of the legal profession dedicated to moving the contract eradication process along.
If real estate law worked the same idiotic way the legal system deals with marriages, you'd never see another piece of property bought/sold in this country again.