There's no way to argue for or against gay marriage itself. It just depends on the person. If someone wants to dictate to me that gay marriage is legit marriage, I will not accept that and will lose respect for that person for trying to force a personal belief, but that is a different issue from its legitimization under the law. For that, do whatever, but if you must ask me, the answer is NO because of what the gay rights groups do.
Aren't YOU trying to force your personal belief on me by being against gay marriage? You've got a very flawed argument, there. Especially considering that you continue to claim that you're against gay marriage because of what gay rights groups do. Shouldn't your opinion be based on, say, the merits of actual gay marriage rather than the behaviour of certain groups that advocate it? That's like saying you chose not to buy a car because you didn't like the commercial, despite the fact that the car, itself, is actually a very good car.