Let's look at two controversial tweets:
The blood is on the hands of the #NRA. Next time, let it be YOUR sons and daughters. Shame on you. May God damn you.
You may be too refined to say it, but I'm not: I wish all the fucking West Bank settlers would go missing.
Both make implicit reference to very recent acts of violence, a mass shooting in a Navy shipyard and the kidnapping and murder of three West Bank settler teenagers. Both take the form of wishing violence on a group of people (literally) but less literally, what they probably meant to say is something more like this:
"If NRA members' own children were victims of gun violence, maybe they would understand the effects of the policies they lobby for." [This is dumb anyway because many gun owners and NRA members already have dead children as a result of guns.]
"Those right-wing settlers are an awful obstacle to peace. They are taking over land that belongs to the Palestinians. They shouldn't be there in the first place so I'm going to save my compassion for the Gaza strip."
A jussive of this type is one step below a threat. It's something like an indirect threat. If you don't object to these utterances, then would you change your mind if it were something like "I wish a few more asshole abortion doctors would go missing" (after the murder of one of them)?
Of course, the intention of these tweets according to their authors (and defenders) is to make a political point in rhetorically strong and expletive deleted way. The argument is that nobody would take them as actual threats or incitements to violence, or sincere desires. Guth doesn't want anyone else to be shot, simply for more recognition of the consequences of gun violence. Salaita doesn't want every settler to be kidnapped and killed, but for the settlements to be dismantled, etc... The pro-life tweeter would say he just wants abortion to be illegal...
Because in their literal form such utterances are desires for more violence to occur, they stand at the very crossroads of where incivility (or mere rudeness, lack of social refinement) is separated from "fighting words." Where you draw the line, dear commentator? What I argue should be protected (as academic freedom) is different from what I personally respect as a form of utterance. I am pretty dogmatic both that all forms of expression should be protected, and that these particular tweets are vile. After all, this form of freedom only exists if it protects utterances that numerous people would object to.