A couple of fallacies with this debate are that: 1. Gay Marriage can be outlawed, 2. It's only marriage if the state recognizes it, and 3. the state's "blessing" of a marriage brings with it a huge package of perks and privileges.
1, There can be no ban on same sex marriage, If 2 men or 2 women want to get married there are religions that have no problem with it, how can you stop them from performing a wedding ritual and prevent the couple from living together? Not just constitutionally but in the physical/practical sense.
2. This part is weird, the state can perform only a secular wedding yet must conform to the guidelines of a religious wedding yet not the other way around. Yes, two men can get married but Only In A Church! If the state didn't recognize your marriage would you not still consider yourself married? Would you not behave in such a manner?
3. This is where the legitimate argument takes place and mostly along the lines of Joint filing taxes and shared health benefits. The second of these is not a gay rights issue but a nation wide health care problem that affects us all, if the current health care system were good working order nobody would care about this. The joint filing is an advantage but still, it's not as if the government is giving away free vacation packages to the Bahamas. Though it is enough for a project moped :)
We live in a country where 50% of marriage ends in divorce, we have way bigger issues to deal with on this front.