To put another spin on this thread:
Sonny's gaffe, and the greed it betrayed, was the cornerstone of Sol's decision to kill Vito. Sol was convinced that Sonny could be persuaded to settle with him, rather than to go to war. No doubt that's exactly what he told Tatt and perhaps the other Dons: there will be no war because Sonny is hot for my deal.
Suppose Sonny had kept his mouth shut. Do you think Sol still would have attempted to kill Vito? Would the others have gone along with it?
Good question. I think Sol would have pushed to eliminate Vito whether Sonnny had run his mouth or not. It was telling that Sol said to Hagen that "Sonny was hot for my idea," AND "YOU KNEW IT WAS THE RIGHT THING TO DO." The second part of this shows that Sol was convinced that the had a tough issue on their hands, and they could be divided and conquered over the narcotics trade. Again, we have evidence of this by the comments made by the Detroit Don at the meeting when he talked about how he paid his people extra not to deal drugs, but it still didn't work because, "they can't resist."
Still, I have serious doubts the other families would have gone with something as exteme as a hit on Corleone. No one really wanted a full scale war, and I think what would have happened was that the other families would have gone into the drug rackets without the Corleone political protection and then chipped away at their terriories. Hagen, when he briefed Sony and Vito on the issue opined that if the family did not get into the drug business it would have an adverse affect on their strength after five years, at which time the other families could then go after them
