Ah, that's why Napoleon is taboo. Because he killed mostly Europeans.

...

This is a rare L; Hitler is mainstream taboo because he is one of the few figures of the few movements which is associated with industrialized genocide as its core cause.

There are a lot of genocidal shitheads who don't get the infamy they deserve in history, make no mistake, and some of them skirt by because of racism. But Hitler being Enemy #1 has much more to do with how and why than where.

... though, related to the trio mentioned, that Churchill is excluded from the likes of Leopold in the popular imagination is certainly a travesty. Four years of service does not redeem forty years of inhumanity.