I think the discrimination of the Italians in America were good for the mafia. Smart Italians couldn't get a job in the legal world, but they could get a job in the illegal world: the mafia.
And that Italians stay within there own group. They dont trust the others. So the Italians in Little Italy wouldn't go to the police but to the local mobboss.

I'm talking about the eraly 1900's