3400 lynchings in 70 years. Hideous abominations, for the blood and torture lust of crowds. But blacks kill more than that many blacks each year.
Slavery enforced illiteracy, broken families, and made it very difficult for most slaves to reap any benefit from their labor - it promoted laziness. So why would a free people continue in such chains?
Armenians, say, the underclass for centuries under the Ottomans, came here as refugees from genocide. They may still be haunted but they've succeeded. Or Jews, or the Vietnamese.