Yes and no. Yes, gay marriage, no marriage should not be legal. Or put more eloquently, I don't think marriage should be a legal thing. In my opinion, you should have to go to the government and say, "Yep, we want to get married. Gimme license." I don't have a particular reason why it shouldn't be a legal thing, but I don't know, it's just one of the many things that I think the government should be allowed to control.
I hear many people prefer for marriage to be decoupled from governmental policies. Benefits like insurance, mortgage, child adoption, health etc. can rely heavily on whether a person is recognised as married. So they'd rather the government instead craft policies around the bigger umbrella of "civil unions", which will encompass the "untouched" male-female marriage, along with the same-sex unions.
I think government should have no say in who you marry. This proves that the government has too much control in our lives.