A general call for someone's death has never been ruled as fighting words in the history of US Law. But I don't think that was really your point.
The thing is, I see people calling for the death of Donald Trump all the time. I don't think that means he's morally justified in killing those people.
That's effectively what this comic is arguing, but in reverse.
Look, I hate Charlie Kirk as much as the next guy, but that doesn't mean we need to say that assassinating him was a good and just call.
He can be a loathsome PoS, and shooting him to death extrajudicially can be a bad thing. Both those can be true at the same time.
I don't have a problem with the comic in the sense that I think the author should be shot, in the same way that I can have a problem with Charlie Kirk and not believe he should be shot.
I can disagree with people without wanting them dead, shockingly.
Kirk was trash, but that doesn't justify an extrajudicial killing.