We can all agree it's immoral, but it's also just plain stupidity.

Even if you are white supremacist "kill all people of color", you still need a professional military that's not wasting time massacring civilians and creating PR disasters daily, if you hope to win any wars at all.

Also "their place in history is settled": sorry to ruin your day but that's not how collective processing of historical trauma works, nor history as a science.