Black Americans were given many chances to leave if life was so bad. First it was boat trips to Liberia. Then there was Marcus Garvey with more boat trips to Africa. Then there was Malcolm X who explicitly defended separation or at least wanted a single U.S state for themselves.

For nearly 100 years, they rejected all of this and instead, moved into White Neighborhoods instead.

Why should anyone feel sorry about this? They all voted for integration, they got it. And they're still not happy just proving nothing changed.

Edit: Not to mention, there where other 2nd class citizens in the U.S during the same time who still manage to make a life for themselves. The Japanese, Italians and Germans were all sent to internment camps during WW2. Yet do we hear about those groups complaining about the U.S today? Nope.

for example regarding lynching.

The story of lynching is they targeted criminals. And it has always existed in more places than just the U.S.