The fact that some Americans supported slavery in the eighteenth century is not at all remarkable. Most of the world agreed with them. What is remarkable is that many of them sought to abolish slavery in the new republic.
People object to government involvement in issues of discrimination, and justly so, but government is already involved to the hilt, and Trump's Executive Order on Race and Sex Stereotyping seeks to take several steps back.
Historically, Europeans had few qualms about conquering and enslaving other Europeans. This presents some problems for the narrative claiming that injustices committed by Europeans are motivated primarily by racism.
Silicon Valley and the media are moving even further left. This is what is to be expected when a single ideological group controls educational institutions and major media outlets over a period of several decades.