Racism and sexism are still alive and well on JWN I see...
It should be surprising to see the violent assault of a teenage girl who broke no laws and exhibited no violent or threatening behaviour not just defended but praised, but when that teenage girl is black it's basically par for the course around here.
I'm not even sure it's racism. It's known psychology for people to attempt to put systematic blame on the individual. This is because it's an uncomfortable thought for them to realize that their life is luck of the draw, and if they were born in slightly different conditions, they would have ended up as screwed up as those people. The illusion of control is really important for many.
Keeping a whole illusion of control up is important for people to feel that life is less random. It's the same psychology that leads people to victim blame the person raped or robbed, and other such things. It's easier to jump on "that person must have done something wrong that I would not have done in that situation" as opposed to confront the fear that you could be on the receiving end of complete bad luck outside of your control. That showcases itself as an automatic defense of authority and skepticism of the person who states they're wrong.