There s always gonna be some groups who gonna try to seize power when SHTF, no matter what names they gonna have, and causes, but in great majority methods gonna be bad. And point is to stay out of the groups with that methods, especially in urban settings.

They not gonna call them selves gangs, they may be “freedom fighters” or whatever, fighting for “cause” or to restore the “order”.
I have seen many of those groups, bad experiences.