I think the whole don't join or risk being a target thing is bullshit. Every member of every gang is a target, so why even be affiliated if you don't have aspirations to be a full-fledged member someday, unless you're a semi-legitimate businessman acting as a front. If everyone has that mentality, then yes the Mafia will shrivel up into nothing. Prison and death comes with the territory, if you're that damn scared of being a target, don't even get involved in crime in the first place.