That's a completely different issue: if you have a tourist visa or visa waiver, the rules are indeed clear - do not work.
But this article highlights that the rule of law did not apply to this student. Again, it's not about the rights or wrongs of political engagement abroad! It's about what the rules allow you to do whether or not you are a citizen in the US. It's really not that hard to understand why it's a problem.
...Because of course, once they normalise this, they will come for anyone with an opinion. Then what? Will you guys say 'sure, you can't say that stuff out loud, that's on you'? Because that's the definition of totalitarianism.