The looters acted like looters. It is not reasonable for you to continue to conflate the two.
For some reason you think the two are two distinct groups, when there is certainly much overlap. A person who commits any vandalism or looting (or shooting for that matter) as a form of protest is also a protester.
I don't think the looting was a form of protest. Rather, it was scumbags that looted when they saw a chance.
The arson is a form of protest and those who did it should be described as protesters.