Why's it surprising that there would be gangs of Jews? Well... it would be surprising here, considering there are no Jews here at all, but in a place with a dense Jewish population, sure, why not?
Anyway... most neighborhoods are shitty or getting there. People are crazy, and not in a good way. And if you have what could be considered a nice neighborhood, then it will just attract assholes from much worse neighborhoods who will screw it up as they have their own. What can you do? Deal with it until you're old enough to move, I guess.
EDIT: Jews wear crosses?!?!
