One serious problem most governments face when dealing with organized crime is that membership in a criminal organization such as the Mafia, is usually not in itself illegal. There is a worry about telling people who they can and can't be friends with. Certainly if a person in the Mafia aids another member of the Mafia in committing a crime, or conspires with them to commit one, they'll go to jail for that, be we're not allowed to just arrest them for being Mafia members.
I think that's silly. Naturally we have to draw the line carefully, but I think we can do that. It's not so hard. I think the way to define allowable and not allowable associations is to zero on a few questions:
1) - Does it have a command structure?
2) - Does that command structure have effective means at its disposal to force members to obey its commands against their will?
3) - Does that command structure routinely give orders that contradict the law?
Putting oneself in a situation where they are no longer free to choose whether they will obey the law or not should definitely be a crime. We outlaw drunk driving because a drunk person at the wheel wouldn't have enough control over their vehicle to prevent doing harm to others. If by being a member of a criminal organization a person finds them self in a situation where they may be threatened with harm to themselves or their families if they don't obey a particularly heinous order given to them by a superior, then at a minimum we could say that their free will in the matter has been compromised. Maybe they don't have a choice now, but what about when they joined?
How often do criminals who do horrible things say "Oh but my leader would have killed me if I didn't do what they said!", or leaders argue that if they weren't brutal enough their underlings would oust them. Clearly the crucial point where the decision was made is when the person joined an organization that they knew full well was likely to give them those kinds of orders. At a minimum it's an act of reckless endangerment.