Perhaps it's you who aren't so familiar with circular logic if you can't see it.
You're arguing that gays can't get married, ostensibly because the law only allows marriage between a man and a woman.
Well, if the law is changed to allow marriage between two people of the same sex they could.
Well, but the law doesn't say that.
Yes, I know but it could.
But marriage is only between a man and a woman.
Yes, but... nevermind.
Circular logic.