Maybe you have an aversion to logic, or maybe just to the obvious, but if the law defines marriage in a way that precludes gay marriage, there is a law against gay marriage.You are the one with logic problems.
Following your logic, are you saying that there is a law against me collecting veterans benefits?
I've never served in the military, and I'm probably to old to serve now. Since the law defines veterans in a way that precludes me from being a veteran, there is a law against me collecting veterans benefits. That's not fair. We should change the law so that anyone can be a veteran, regardless of military service.
There is no reason that gays can't get married. However, if it isn't a man and a woman, it's not a marriage. How difficult is that to understand?