Sicily was too small for Vito to have eluded Ciccio.
Do you think so? I mean, we're talking about the early 20th century - no cars, no public transport. Siciliy is more than twice as large as Hawaii and has 5 Million inhabitants. Even Michael managed to hide in Sicily for more than two years, and even before his wedding he must have been known as "The American".
Fanucci must have reminded him of Ciccio--and the danger of giving into "black handers."
I think Vito had learned early that he has to fight for himself in his life. New York was a dangerous place anyway, with or without guys like Fanucci. If you were poor and you had nothing to lose, why not become a criminal. Vito's violence emerged slowly. He witnessed violence in New York everywhere. Clemenza hid guns at Vito's place. When they stole the carpet, he saw that Clemenza was willing to kill a cop. And after all, when they were robbing the trucks, Vito must have held a gun against others, which means he must have been ready to kill.
By 1945 he had perfected the lie about himself: "After all, we're not murderers." They were!
