None of you have provided any reasonably objective definition of what could constitute an otherwise illegal, and sometimes violent protest.
These responses sound a lot like right-wing NRA 2cnd Amendment people barricading in buildings with guns and police surrounding them kind of rhetoric.
All three of the responses (at the time of my response) purport arbitrary definitions of self-determined, extra-judicial action - essentially vigilantism.
Literally, people inventing some cause and then taking over public property, sometimes causing damage, or worse.
If you accept your own definitions of 'legitimate cause' - I'm afraid you're really not going to like what a lot of other Americans would like to protest, just as violently.
If people are going to protest, especially when things can get violent, they're going to have to do so in a way that's not entirely disruptive -> like gather in a park, otherwise, it's just not going to work out.
We don't get to invent the law, no matter how passionate we are about something.
There are just a ton of better ways to create change that are totally within civil and legal framework, and there are many good examples to follow. And especially the rioting is probably counter-productive in almost every sense of the terms.
By your definition, black people using or destroying a whites-only bathroom as a form of protest would be off limits. I'd recommend some time away from the keyboard and do some reading about protest and the cultural history of same. As a very basic starting point, you might consider reading https://en.wikipedia.org/wiki/Protest in its entirety.