Sam, and all the other mobsters, prayed upon the weak. That's it, the rule of all mafia's: the law of the most violent ones.
A completely deranged Sam with an army to back him up against the weakest of the Chicago juice-market? Not a chance. His victims weren't apoplexy with muscle, just losers with nowhere to turn. Not self-assured guys ready to defend themselves, and if they were, he'd take some guys with him. He wasn't the smartest, but wasn't that stupid.