Lego
Unfortunately the demographics of the gangs are nothing like what you would need to sustain such a simplistic conclusion. Those street gangs, as you call them, have as many Anglo members as they do of those with middle eastern Arab heritage.

The whole ethnic argument bears no scrutiny

But if you insist, it is commonly known that the biggest users of heroin are Anglo - skips
One of the reasons the Muslims beat up on them Is precisely because of their heroin use and street loitering.