Selling loosies, tagging, rolling bones in the alley, etc. It's all small stuff. Nobody should hassle with it.
Except that it never ends there.
One day someone gets pissed someone moved in on "their" territory and throws a punch. The "victim" comes back with a motorcycle chain. Next thing you know there's a gun, sad as it seems, little Suzy who was just playing on her doorstep gets an "accidental" bullet in her head.
You can't just let "the small stuff" go. All that does is set a precedent for bigger stuff.