It's an interesting question. Here's my reductive, off-the-cuff take: violence is justified when defending oneself or another from imminent bodily harm, or even under threat of imminent, considerable property damage. When a threat is not imminent, or an action is past, we use the police and the courts, because we as a society–in the sense of subscribers of the US constitution or similar tracts–believe that it is better to have a judicial system and impartial officials determine whether it is worth depriving someone of their bodily liberty or taking their property, that is, jailing or fining. Taking some sort of extrajudicial action or applying corporal punishment (!) requires a much higher bar. How and when would one determine that the judicial system is so unreliable as to morally permit vigilantism? It requires a great deal of moral self-confidence to take matters into one's own hands.

I focus on the question of vigilantism because that I think is the issue. Many people feel an emotional impulse, that they want to side with the CEO killer, for example, and they find ways to rationalize. What I'd say is, if you think Joe Blow is so evil , why don't we take him to court? What kind of possible actions could we not jail or fine him for but for which we would accept Johnny Anarchy, y'know, igniting his lawn furniture? Of course, the justice system is imperfect, but nobody lawfully elected the next sexy assassin as judge, jury, and executioner.