Everybody peddling some kind of mob justice also has high self-esteem?

The existence of mob justice has more to do with the failures of the legal system. Many times in history, when the populace feels that they are not getting "justice" from the legal systems in place, the populace turns to mob justice because the systems they rely on fail to mete out justice in any comparable way.

When cops can kill with impunity and are never subject to the laws they enforce, you have people wanting mob justice.

When politicians can lie with impunity and hide behind free speech and keep their jobs, their benefits, and all, you have people wanting mob justice.

When corporations can send bomb trains into your city, poison everyone within hundreds of miles, and then walk away with bonuses for covering their asses, you have people wanting mob justice.

These are wildly different things. Trolls are doing it because they want to hurt others, a lot of people are doing it because they want to stop being hurt by a system that has decided they don't deserve justice.