"Racists will say the "blacks" are inferior they're more mature (like here), but then they would also say "blacks" are inferior because they're less mature."
To be fair, what our enemies mean is that "black" children reach puberty at an earlier age on average:

but "black" adults have lower sexual dimorphism than "white" adults (due to the latter having a heavier puberty) on average:

In short, our enemies think that "blacks" are inferior because "black" children aren't really children and "black" adults aren't really adults, just like they think "blacks" are inferior because "black" women aren't really women and "black" men aren't really men. We could say that Western civilization, in addition to valuing high sexual dimorphism, also values high pre/post-pubescent dimorphism. This is consistent with Westerners being not only homophobic and transphobic, but also MAP-phobic.
We also see this in how, at the same time as Western civilization is praised by our enemies for having fiction with the most adult themes:
https://trueleft.createaforum.com/human-evolution/sexual-dimorphism-preferences/msg16234/#msg16234it is also only Western civilization has an explicit category of fiction called "children's fiction". In every other civilization prior to the colonial era, it was considered normal for children and adults to consume the same fiction.
Even the stupidity known as:
was a Western idea:
The British Board of Film Classification (BBFC)[3] is a non-governmental organisation founded by the British film industry in 1912
Ultimately, Western civilization is the most age-segregationist civilization. (Compulsory schooling for children is the most cruel manifestation of this.)