I'm shocked by the amount of anti-miscegenation and not-pro-miscegenation sentiment on this forum
The operative word here is forced. Or, at least, mandated.
Also, forcibly homogenizing the population in *ANY* way, with the most recent variant being keeping the 'races' 100% pure, is ridiculously irresponsible. Even with small variations in a population, you lose a ton of adaptability a 'chunky' genepool has, so you risk outright accidentally exterminating the human race once an epidemic or whatever hits.
For that matter, those differences are not just random variations, but adaptative traits. Removing 100% white people cuts off a variant that is evolutionarily optimized towards the conditions of relatively low sunlight regions like Northern Europe, and black people for very high for instance, and the resulting homogenous mix (presuming literally equal distribution of quantitive traits) would perform worse in *both*. Jack of all spades, master of none.
That's forgetting that a number of traits are recessive, and in a mix, they would be extremely suppressed in the macro-scale. You'd still get, say, blue eyed people, but that would be a random deviation from the mean, not a geographically preserved population with above-average frequency of the allele.
Interracial mixing is absolutely necessary - for much the same reasons, in fact - but the optimal number is neither 0% nor 100%. Possibly not 10% nor 90% either. So just let people screw whoever they want and not start weird mandatory homogenization campaign.