My point is that people who opposed interracial marriage thought that they had a rational basis for doing so (even though it didn't make sense); similarly, people who oppose gay marriage today also think they have rational bases for doing so, even though they don't make sense.

> they can be rational and maintain that a relationship between two people categorically incapable of producing children together biologically, two people of the same sex, can’t be a marriage

Pretty much nobody actually makes this argument, though. Probably because infertile people get married all the time.