When do you think violence is justified?

Self defense. But also like someone else said proportionate response is key. If someone gets mad at you in a bar and throws a punch, pushing him away is fine. Hitting him to subdue him is probably okay. Shooting him dead is not.

I'm also not really okay with people using murder to defend their stuff. Like if someone sneaks into my house and I catch them going out the window with my tv, shooting them is not to me justified. There are more TV's. That guy gets one life. Remember what Gandalf said.

I think a lot of people have like tough guy fantasies about shooting a burglar and it always makes me uncomfortable.

On the other hand, if someone was on trial for shooting a Nazi dead I would find them not guilty. Shame that Nazi spontaneously bled out. But at least he's gone before he killed my entire family and friends.

When the rich break the social contract.

When someone who I was supposed to be able to trust kept repeatedly trying to record me naked in the shower, I retaliated once by kicking him hard in the face. I was told that what I did was wrong and violence was never the answer. I disagree.

Punching nazis. Always acceptable, even encouraged.

Nobody else has mentioned proportionality.

When responding to aggression, the response should not significantly escalate the risk. So lethal force should only be applied in scenarios where there is a lethal threat, etc.

Self defense, as part of a game (such as wrestling) or in BDSM, when both sides are okay with it and don't face actual danger.

Self défense, yep. On a battlefield ? Let these old fuck fight one vs one to resolve their conflict. A noble end is so fucking subjective that I think it would be a terrible idea.

Violence is justified when you have no other means left to defend yourself or someone else otherwise.

At which point I would like to add that people will sometimes not be able to see the means they have left because they are put in a stressful situation in a second. I feel like you can't really blame them for that.

Violence as a response should always be in proportion. That should avoid escalation. In an ideal world.

Unfortunately some people won't stop. Those people need to be put into prison where they cannot hurt anyone anymore.

Use of some violence is justified to stop another bigger, ongoing violence.

I heard a quote that has really stuck with me, it goes something like "violence is the supreme authority from which all other authority is derived"

I don't really condone violence, but this quote has really gotten me thinking.

Bhikkhus, even if bandits were to sever you savagely limb by limb with a two-handled saw, he who gave rise to a mind of hate towards them would not be carrying out my teaching.

I live with this in mind every day.

Much more often than I actually do it.

When you are the victim of a loot ninja

Violence, by definition, is an unjustified use of force. If a use of force is justified then it isn't violence.

For example, suppose you're walking across a bridge and you see someone about to jump to their death. So you run over, pull them back from the brink, knock them down, and sit on them. Have you committed an act of violence? I would say not.

On the other hand, suppose the person is just standing on a street corner waiting for the light to change. If you run over, pull them back from the curb, knock them down, and sit on them, that would in fact be an act of violence.

when someone is WRONG on the internet

To protect against violence

Yes.

Self defense but also including defending your rights, freedom, property, and sovereignty

Violence is a form of escalation. One should never cause a conflict to come to a new height and should only resort to something if in response to anything of that same height.

Also, if a ruler of a nation resorts to that, it shows they're not a great/effective ruler. Fluency in how to rule is determined by how much peace you can accomplish with as little change as possible. Less is more, as they say. If you have to punish people too often like some are doing, you're violating that "less is more" rule.

Self defense

Usually never.

It's always a matter of degrees. The bigger the injustice, the more violence is justified to rectify it. It is in the disproportionality, in my view, where the problem arises.

Never forget that humans are just barely evolved apes. Sometimes a swift knock to the head is required to activate those neural pathways to discourage anti-social behavior. Not always, but also not never. Claiming otherwise is just self-aggrandizing moralization that people use to make themselves sound and feel superior.

this is where the mythological concept of sin sorta helps. So its a bad thing but basically you decide at what point doing the bad thing is worse than other bad things but you can't ever make it not a bad thing. You just accept its price at some point and its ultimately and individual decision and I don't think many will know until that moment. For myself I try to avoid it as much as I can but I don't know in what situation I will be driven to it.

When folks are mean to service staff.

Striking someone that could cause lots of violence to others otherwise...
Of course violence would be the last resort in this case as well, in my opinion, but it would be the lesser evil.

Some people use violence to fuel their morbid curiosity.
Can it help an individual who delves into such topic through discussions and material?

I think it is hard to list all the situations but in the end it boils down to situations where both you personally as the person considering using violence and the average person could live with that decision in the long term. Both because that covers situations where you personally are a lot less or a lot more concerned with the consequences of your actions than the average person. And the average person instead of every single person because there are always some individuals whose views on the matter are a bit too extreme to be practical. Maybe instead of the average person it might make sense to use something like "90% of the population" but in the end you can't measure things that accurately anyway.

All of the above that you listed

Self defense comes to mind, but probably there are other examples.