As you do the Corleones' dirty work and claw your way up through the organization, you'll quickly learn that there's more to organized crime than thuggery. Being a mobster isn't all family dinners and gruesome hits, after all, and so you'll spend a lot of time doing stuff like muscling in on gambling rackets and convincing shopkeepers that maintaining a good relationship with the Corleones would be in their best interest.
Okay, maybe that's still thuggish. The point is, if you're going to make it as a big-city goon, you'll need to learn to push people only as far as the breaking point. Intimidation, threats, and destruction of property will get you what you want more often than a bullet will, and some people might even give in without a fight. And if the people you're trying to shake down still won't listen to reason, well, you can always knock their teeth out.