I think it's what is missing in the article. Anger incorrectly directed is a bad thing. But the article implies that there is no correct direction to the anger, which makes the article sounds as naive and misdirected as people who get angry at the wrong persons.

I would even say that being angry at the wrong person is as bad as not being angry at the right person.

Being angry is a societal tool to put limits on what can or cannot be done. If there is no anger when people crosses the line, then there is no real signal for them to not cross the line. And, no, "a peaceful rational argument" is not an alternative. This is not at all the same signal, this is a signal that is sent way earlier before that specific line and it is exactly how the overton window shifts.