In my opinion, marriage is nothing more than a contract of love and commitment, and I don't need government recognition or acquiescence for it. I also think proponents of gay marriage are more concerned with parity with heterosexual couples, something else I don't need or care. A civil union has worked just fine and asking the government to recognize my union as marriage just doesn't interest me.
The obvious counter is the one already deployed, if only implicitly, in response to your comment - that this analysis is selfish, and says nothing about whether gay marriage is socially valuable, but only whether it's valuable to you.
I spent a day's worth of HN participation arguing against gay marriage, a few months back, and came out net positive in karma. If you're interested in those arguments, they begin here: https://news.ycombinator.com/item?id=12976422
Should you take the time, I'd be interested and obliged to hear any thoughts they occasion.
