I regularly make that joke in response into various abuses of the public by the state. The point is we saw how political journalists can be motivated to expresss outrage (and outrage which won't get them fired). One of their own - in this particular case, Maggie Haberman's close conspirator, I mean "source" - experienced extremely mild social sanction and it was treated as an injustice most foul.
A journalist's job isn't to hold the powerful accountable, you see, it's their job to ensure the public behaves appropriately. It's their job to ensure the public behaves appropriately towards "them."
An addtional issue with the Sanders incident specifically is that part of DC political culture is that spokespeople are just doing their jobs, that they don't set policy, so it is unfair to hold them responsible for it. Maybe it's OK to protest politicians themselves, but not the people who work for them, even the highest profile ones.
The "cruelty" of the public angers you, but not the cruelty of the state?
