When Michael survived and came back, he could have had a "legitimate future" but Vito dragged him into the criminal business

Vito could have retired, and handed over the reins of the Family then, cut their losses and walked away from Mafia, leaving Clemenza and Tessio in charge but he didn't because he wanted, needed the Corleone family reputation, standing, history etc. to be restored, leaving a murderous legacy for Michael even if it meant dragging his never wanted this for you son as Mob Boss