Slavery was never legal in most of the United States, the abolitionist movement was part of the United States' history from the very beginning - something quite unique to our history, in fact - Africans enslaved them first and slave traders purchased them - Africa continued to have widespread slavery of both blacks and whites well after we eliminated it here - the GDP of the non-slave areas in the US was vastly stronger than in slave states so our country was not built on slavery, there were thousands of "free-men" blacks who owned slaves in the South as well, and so on, and so forth. To say otherwise is to be willfully ignorant of history, or lying about it. Slavery is evil - and if you believe it is evil, then you don't pigeon hole this kind of evil to only bothering you if it fits a certain narrative.
He’s not guided by rational, critical thinking.
He’s motivated by his own burning self-righteousness.
His only goal self-aggrandizement.