makes zero sense to me to genderize(?) a whole race/group of people like they're a completely different alien species

Leave it to crackkkers to achieve groundbreaking new heights when it comes to racism

i'm not understanding the rationale behind people labeling blackness as "masculine" and whiteness as "feminine".

My best guess is that the origin of the idea is slavery itself. Work was seen as inherently masculine (women at home don't do real work of course), so the bodies of slaves that were seen as tools for work were therefore also perceived as inherently more masculine