In the places that the parent is describing, the police aren't your allies. The more dangerous the area, the more aggressive and hostile the police (at least to some degree by necessity), and the stronger the "presumed guilty" takes hold, and the more hostile the population itself is to the police.

In the worst of those areas, the gangs themselves take on the role of the police (offering services such as protection, policy enforcement, loans, etc).

Spoken from a true position of privilege! There are many communities where the police and the criminals are both likely to cause you trouble somewhere between a mild hassle and a life-altering interaction. The only difference is why they might do it. Distrust of the police amount law-abiding populations is a thing for a reason.