How did heroin affect italian-american neighbourhoods?

From what I can understand, LCN were the main men involved in the US heroin market from the 1950s (and probably earlier) up until the Pizza Connection trial. I've read conflicting narratives that the mob kept their neighbourhoods safe from drugs and crime, that they only sold it to non-italian nrighbourhoods and farm teams like the Purple Gang were selling heroin in their neighbourhoods. But what's true?