Is their preference really any more arbitrary than the preferences sapiosexuals or demisexuals have? It sounds like they probably have other traits that may make someone more or less attractive, they just have a minimum requirement for a certain body form for them to begin having attraction. That isn’t so different when compared to a sapiosexual who requires a high intellect before they can begin being more or less attracted based on other traits.
TL;DR: All preferences are weird, no need to call anyone out on their specific ones :)
This is an incomplete view of the history of slavery. By the numbers, the vast majority of the people benefitting from chattel slavery were white. However, slave ownership reached similar per capita rates among some of the Native American tribes, and there were instances of slaves being owned by free people of color. Notably, there are a large number of black tribal members in the United States. The United States government signed a number of treaties with the tribes in the 1860s that required them to free their slaves and incorporate them as full tribal members.
None of this is said to diminish the fact that the American system of slavery was a product of colonization by European countries. But it is rather reductive to claim that only white property owners benefitted from the atrocity that was chattel slavery.