Critical thinking skills in a society are anathema to those in power who wish to stay in power, and do so by preying on the fears of others and exploiting the racist/sexist/homophobic systems in place which they continue to uphold.

I was taught about the facts of slavery when I was young. I don't recall feeling guilty or made to feel guilty about it. What I did feel was empathy - it's wrong to enslave people, and the treatment of slaves, was by far, was cruel and inhumane, and should never happen again.

It's much easier to stay in power and keep current systems in place, systems which benefit (the general) you, if you can remove empathy from the equation. Erasing the facts of slavery and its history in this country helps to do just that.