Douglass had it right. The Declaration of Independence set out our ideals as a people — All men are created equal and have certain inalienable rights. We are also humans, and as such are imperfect. We have failed to live up to this ideal, more so at some times in our history than others. The Constitution was such an example. It contains language that recognized the political reality of the late 18th century. Unfortunately part of that reality was that slavery was legal in many states. In order to get the Constitution ratified, this was necessary. It does not mean the Constitution was pro slavery, though, just that the Founders has to bow to the practicalities of their time.
BLM: If you are white, you are a racist. If you are black, you are an Uncle Tom. Anyone who disagrees with us is either the one, or the other. And even if you agree with us and are white, you are still a racist.