Well, if we forget this part of our history we forget about the causes of the civil war as well. One of them was slavery (but not the only one). So let's forget about slavery. Never happened. Now when someone talks about the legacy of slavery we can say, "What slavery? That never happened!"
The left has used this tactic in trying to say that the American life and culture of the 50s and early 60s never existed, so we should stop trying to go back to something that never happened. We simply apply the same tactics to them.
That’s just it, no?
Slavery and the race card...make the history disappear or greatly diminish it...what do they gain? Why? It takes away from their meme.