Rule: Do not attempt to use reason (critical thinking) with people who only live by “emotion”.
History is very complicated, contradictory, messy.
That means if you tell the truth about it you will be banned almost everywhere and hated by almost everyone.
In addition to that advice, I would suggest that you go to the source for information about Frederick Douglass. Read his autobiography, it is enlightening and shows that he was not a hate filled person. He was grossly mistreated so some of the comments about him having it good are ludicrous.