The NAACP pegs the number at 4,743 total lynchings between 1882-1968. 3,446 were black, with 1,297 being white. 79% occurred in southern states.
Fundamentally, a lynching is just a fancy way to refer to mob justice. People get frustrated with the slow and methodical justice system. Rules of evidence can and do let many perpetrators free, and people are well aware of this. There is disagreement over what constitutes "cruel and unusual punishment", and plenty of anger when punishment seems insufficient for the crime. Frustrated angry people tend to take matters into their own hands.
This is something to think about when considering making punishment less severe or easier to avoid. There is a point at which ordinary people won't stand for it. Our justice system largely exists to appease angry people who would otherwise dish out their own idea of justice.
There were also lynchings where the mob simply believed the victim to be guilty but unprovably so. Or where the punishment would not be sufficient to the crime in their eyes. Those are the ones which the GP seems to refer to, and it's not necessarily trolling to bring up the relationship between those and a justice system that is seen to work.