The idea of a nebulous "illegality" is simplistic and wrong, in the US. They might open an individual to civil liability, but they aren't in violation of a criminal code, nor tort law.
> That doesn't mean the action of speaking those words are legal
Speech is always legal, in the US. What you think "legal" means is up for debate.
People protest all the time in similar ways.
Also, you can block people/bots on social media.
Sure, that is why protesters are routinely arrested even though the first amendment exists.
>Also, you can block people/bots on social media.
The sole responsibility of policing and punishing this behavior should not fall on the victims of this behavior.
Blocking someone is neither policing nor punishing, it's simply ignoring; actual censorship still falls to the platform itself.
Around the clock shouting in residential neighborhoods is likely to get you fined for disturbing the peace.
But, you can send hate mail, or shout in some public spaces and be just fine.
Sending angry emails or tweets sounds most like the former.