"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.