I'm not sure whether this applies to all of the specific cases discussed but surely most people would agree that some of these threats are, or at least should be, illegal? I know the US loves the notion of 'free speech' but if you're publicly posting a picture of you pointing a gun at a police car with a caption, "Should I do it?", that seems like a credible threat to me.
If I was just looking online and I saw a picture of a gun aimed at me with the caption, "Should I do it?", I'd seriously hope that there is something illegal about that which the guy could be charged and arrested for.
The question must then be where to draw the line, rather than suggesting that the entire approach is wrong. Like if a guy was arrested for "liking" some of those comments, then that seems maybe over the line to me. But threatening someone, whether in real life or online, seems like it should be a crime to me. I don't see how it could be described as "dissenting speech".
Obviously it seems stupid that they're focusing so much time and effort on cutting down verbal threats to police when they can't sort out the police actually physically assaulting and murdering black people though, so I can see why some people would be angry at this particular blitz and its timing.