Earlier quoted context omitted.
> The "leader" is an avowed racist and nasty person in general. Oh, good. This again. Curtis has stated publicly, "I am not an 'outspoken advocate for slavery,' a racist, a sexist or a fascist." See: https://medium.com/@curtis.yarvin/why-you-should-come-to-lam...
Anyone can say they aren't an outspoken advocate for slavery. Take a look at this http://unqualified-reservations.blogspot.co.uk/2009/07/why-c... and see whether you find it plausible to say that the author is not an outspoken advocate for slavery.
The passage most frequently cited as evidence of this charge is:
Thus, Spaniards and Englishmen in the Americas in the 17th and earlier centuries, whose sense of political correctness was negligible, found that Africans tended to make good slaves and Indians did not. This broad pattern of observation is most parsimoniously explained by genetic differences.
A charitable reading of this, in my mind, goes:
Some slavers had an opinion about who made good slaves and who didn't. If one wanted to rationalize a basis for that opinion, which historically existed, the easiest/laziest answer would be genetic traits common to the populations in question
Check the definition of "parsimonious" and assume the author used it on purpose.