Geeez, maybe I can help here.
The two things he is comparing are NOT groups of people. He is not talking about blacks as a group (or individually). He is not talking about gays as a group or individually.
He IS talking about arguments used to justify a position. He is NOT talking about arguments blacks have used and he is NOT talking about arguments that gays have used.
He IS talking about
arguments put forward against selected marriages. Get it? Arguments NOT groups of people.
He IS comparing the
argument you have used against selected marriages to
arguments used by some whites (like the KKK I am pretty sure) against mixed race marriage.