He defends what he posted under Mencius Moldbug in a Medium blogpost here[0], which is nominally level-headed. There are in fact genetic differences across ethnic groups (sickle cell anemia comes to mind immediately), and it would be silly to think that the only possible generic changes are changed skin color and a specific blood disorder.
You can say that since men have a statistically higher muscle density, they are genetically better slaves than women are. That does not mean that I'm advocating we enslave all men, or that slavery is anything other than abhorrent.
Everyone focuses on something, if you want to extend your argument he should have also focused on diet, type of exercise, type of housing slaves are kept in, etc.
Focusing on every single factor that could possibly effect slavery would be an endeavor probably greater than the average lifetime.
Saying that some group of people or another would likely make better slaves than others is no different than saying that a certain group is more likely to be poor than another or be in jail than another. It may be considered in bad taste to discuss, but it isn't morally wrong to discuss.
It is simply remarking on what is, not what should be.
You can say that since men have a statistically higher muscle density, they are genetically better slaves than women are. That does not mean that I'm advocating we enslave all men, or that slavery is anything other than abhorrent.
0: https://medium.com/@curtis.yarvin/why-you-should-come-to-lam...