Most opposition to interracial marriage probably is latent by now. People probably are completely fine with it if they see it on TV (or they think they are)
But it isn't really shown on TV, and it doesn't really happen all that much in the real world, probably an order of magnitude less often than would be expected if you had simply random pairings. It's not like homosexuality where you had more gay people and couples in the real world than you saw on TV until relatively recently. TV producers know that miscegenation is not a question with simple answers for most people, even if the vast majority of the population genuinely believe that anti-miscegenation laws and the like are wrong and should not exist.
