With any luck, one of the present gangs wiill become top gang in a area, like the Krays, the Richardsons, and going back, Jack Spot and his cronies, and then all will be sweetness and light, all locals sleep sweetly in their beds, and no old ladies will be mugged on their patch.
That's the logical conclusion , based on the premiss of the OP, isn't it? Or have I missed something ? Just don't call any Mr Big 'a fat poof' or you may end up dead in a pub toilet .
Gangsters liked to keep local petty criminals in order. The last thing they wanted was imore police snooping round their territory. And, as a bonus, it kept other locals happy and reluctant to say anything about them. Good PR, see?