Is extending marriage rights the answer?

New York's Governor says he is preparing to introduce a same-sex marriage bill into the state legislature in the coming weeks. I support equality for all people regardless of gender or number of partners. I have serious reservations about reinforcing marriage as the qualification for receiving all manner of state-sponsored rights, benefits, and considerations. At the same time, for now marriage is that qualification, and everyone should have access to it. So, is the next step to push for recognition of polyamorous marriage, or is the next step to begin the undermining of marriage as a core civil institution?