We use a lot of euphemisms and have a number of myths around political violence. The fact of the matter, so far as I can see, seems to be that political violence is extremely effective, however also extremely destabilising if used at scale.

Force just works a lot of the time, assuming you can win, and often even if you can’t, as even imposing a cost on your opponent often gets you a better deal. There’s a reason we keep having wars.

Also realise that the government monopoly on force is ultimately the only reason that anybody follows laws. That following laws is good for us is beside the point - force must be threatened and used in order to maintain control.

So, force, a euphemism for violence, is ultimately the way anything gets done, and we all have an incentive to lie about this just for the sake of stability.

I don’t know if this answers your question, but it’s what comes to mind on the subject for me.

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.

Because life is not black and white, and people often agree, that humans who actively work towards the detriment of society should not be part of the society.