And those mechanisms, the military, the police, and the legal system, rely on violence as the ultimate fallback when other options fail. So you may not be relying on violence to solve your problems, or the threat of violence, or the insinuation of it, but instead relying on the threat of someone ELSE’S violence. That is the social contract pretty fundamentally. And when people can no longer rely on those figures who are supposed to use violence on their behalf, we shouldn’t be surprised that they attempt to reclaim the ability to use force. The social contract has been voided, in their eyes. The premise and promise broken.

"Let's say you live in an apartment building and your landlord locks you out and keeps you belongings. Police say its not their problem. Courts decide that they don't aare either. So now you have no recourse or body to complain to.

In that situation saying "i resolve problems non-violently every day" stops being relevenat. The mechanisms that allow you to do so (enforcement, law, etc) have been removed as they were for those fighting for civil rights.

You may still personally choose non-violence in this case, but I'd bet you would understand/sympathize/maybe-even-join those who decided to break into their apartments by force and grab the things that are rightfully theirs."

I would say it depends. Are there depts of rent involved in that scenario? Did the locking out just happened out of the blue, or was it communicated before, that it would happen?

Apart from that, I surely see more easy examples of justifying violence - for example to stop other violence.