i would never fall into that trap. I'm no William Shockley and I protested his talk on our campus decades ago. The argument is that in-breeding can build weakness. Witness Spanish kings and cleft palates centuries ago. I would think there's evidence with ancient Pharaohs as well. Mixed breeding permits further evolution, either strengthening what promotes survival or mutating it either out of existence or another step above the ladder. I would say the same for cultures. The same argument applies to freedom of thought. In the old days, before the Iraq war, I got much more out of conversation with what few conservative friends I had than those who agreed with me. Maybe I'm wrong but this is my understanding of natural selection.
I know a physician in Thailand, the owner of several hospitals, who made a version of your argument about mixing my blood with my bride to be. On average, she said, the product would be more intelligent than of one of what we falsely call similar race.
I'll venture into the political implications of what I said. Of those voters believing in or advocating anti-miscegenation laws a higher probability of them voted for Trump in the last election. That can't be verified, of course, but you get the drift. It could be verified in a future election by examining trends in, say, North Carolina now.