Aristotle's point was not that "races should be introduced", not that that would make any sense to him anyway, his point was that dissimilarity in a society, especially a language barrier, is the best way for a tyranny to operate.

Interbreeding humans from different racial groups doesn't effect that one way or another, if that's the extent of the equation. Now, if none of those speak the same language or share the same culture, that is when authoritarians seize power.