I’m not sure that justice was the goal here; what the RIAA does is not illegal, and nor are the annoyances and other shunning behaviors that were suggested.
I don’t think “vigilante” or “angry internet mob” are accurate descriptions, either.
You don’t need to be angry, or a vigilante, or seeking “justice” to wish negative consequences for certain (legal) choices made by others in society, such as working for the RIAA or other such jobs that make our world and society worse.
It’s a false dichotomy to think the only two options are “do nothing to hinder them” or “angry internet mob”.
Legal, harmless ways of discouraging certain choices are perhaps one of the best tools available to us for improving our society, in many different contexts.
Making dubious legal arguments and demands is what the sovereign citizens do and that's the same thing as what the RIAA is doing here. We shouldn't legitimize their techniques because it's couched in a pseudo-legal framing, but we should engage in action-for-action.
You should not conflate the two.
Creating negative consequences for poor choices in society is a great and effective tool that should be used more often.