In a civilized society, we all have a social contract that says " law > opinion ". That's why morals don't matter when deciding to punch someone or not. Want to punch a Nazi? Go get your legislator write a law about it. Simple.
We cannot just have everyone randomly going off Robbin-Hooding around based on their own morals and half(at best) understanding of complex issues.
In this specific case, a couple things are at play. I don't think people thought "I want to punch Nazi's". They thought "Richard Spencer is gaining power via confidence and support, I want to send a clear message". I don't agree with the action they chose for it, but that was likely some form of the logic. However, they may have resorted to the action because they didn't believe the law could help them. People are losing faith in the system fast, and frankly for good reason.
We cannot just have everyone randomly going off Robbin-Hooding around based on their own morals and half(at best) understanding of complex issues.