I am well acquainted with the myth of race. Ashley Montagu addresses that myth in detail in his book;
Man's most dangerous Myth: The fallacy of Race.
The book validated my inclinations to believe the term "race" has power only because most people believe in the pseudo scientific term. I don't! However, I am compelled to use it myself without really wanting to in order to converse with those who believe in race.
That belief in race was the causal factor in the dehumanizing aspects of slavery. Sure,, poor Whites endured slavery and indentured servitude also, but when whites enslaved other whites there was always the human nexus that kind of tempered down the general treatment of White slaves. Blacks were dehumanized and relegated to a status little better than livestock. That world view was so pervasive in the white world that even today remnants can be felt and seen everywhere Blacks and whites intermingle on some level. The illusion of race persists despite scientific evidence to the contrary and White people continue to attach an inferior component to the Black "race" either consciously or sub consciously.