Norm is relative and defined by those who use that term.
When dealing with frequency, any recurring event of police brutality is unacceptable, as with any crimes. With police brutality, however, it is extra evil, since those guilty are the ones who are given public trust, unlike the common criminal, who has none.
so now we're getting somewhere
if you say it's the norm, then it's the norm
I get it, what you say goes...