Race mixing is like mixing your favorite drinks. 9 times out of 10 it's a little or a lot worse. But 1 time in 10 you get something better, and if that new thing survives the standard, then you've got yourself a positive evolution.
Race mixing is a large short term damage to inclusive fitness, but is also a purchase of a low probability event of a positive evolution, which if successful will keep your race (Or more specifically a hybrid race) the standard as we march ever forward toward colonizing the galaxy.
The reason race mixing feels wrong is because the K multi-armed bandit problem usually yields a loss to the player and a low probability chance that 1 person earns a billion dollars.
Armies of people put their bodies into the bone crusher for that 1 in a million chance.
https://youtu.be/e3L4VocZnnQ?t=5 