I don’t think anyone means anything good by racism, so your multiple definitions are nit-picking.
But in any case, no, that’s not what conventional means. Conventions are commonly-agreed standards or practices. Revulsion (or any emotional response) at mixed-race marriage is not a convention. Only a tiny minority of people have an explicit argued position against mixed-race marriage, and those people are fuckwits: their position is rejected by science, theology and common sense. It could only be described as conventional within a tiny isolated community of inbreeders: not New York.
Anyway, it’s beside the point whether Cohen is himself definable as a racist. The problem is he’s a poor writer: bullshitting wildly, attributing horrible racist attitudes to vague categories of people only identified by an inaccurate use of the word “conventional”, and then denying all responsibility but loving the controversy.
If you knew a prick like that personally, you would weary of their endless self-satisfied shit pretty quickly, I’m sure.
