Until it happens to you.
I must have missed the part of the story where this guy got a fair trial from the folks who tarred and feathered him. No trial, no justice.
I understand the urge toward so-called "street justice", but a community where a person can arbitrarily be seized and punished by some group of self-appointed enforcers of the law without an opportunity to defend his innocence before an impartial court is no community at all; it is merely an organized mob. If the police and courts are incapable of providing an accused lawbreaker with a fair trial, then it's up to the people in a given community to establish some sort of court and try cases based upon facts. Justice must be procedural or it is not justice at all.
People who deal drugs to children are scum, deserving of the severest of punishments — but allowing a mob to become judge, jury, and executioner is a far greater threat to law-abiding citizens than any drug dealer. Today the mob tars and feathers this guy; tomorrow, the mob might come after you.
Well, here’s the thing. They took it to their local vigilante-type organization, who said take it to the cops. The cops in the area refuse to do anything, so what are the people supposed to do?