That was not an argument it was a point of fact. What arguments to Democrats have, Because Jessie and Al told them to vote that way. You have the attitude not me. I am not trying to convert anyone, just trying to understand voting patterns.
You are not trying to understand voting patterns; you are throwing your hands in the air with classic dismissiveness. Blacks have been voting Democrat long before Jesse Jackson and Al Sharpton. It's been since 1932.
Your distinction between an argument and a "point of fact" is a distinction without a difference: you are saying that somehow, blacks should now vote Republican because in generations past, southern Democrats -- who now barely exist at the federal level -- were anti-black. No such conclusion should reasonably be drawn; therefore your point of fact, though true, is irrelevant.
If you want an actual answer, rather than to rest smugly assured that blacks have no good reason for voting as they tend to do, it's due to the northern Democrats' general support for the welfare state and civil rights since the FDR era. Your job -- our job -- is to make the case that the welfare state (which I use in the academic rather than pejorative sense) has not served black interests and it's time to start looking at other factors when voting.