What do you think was Don Corleone's worst decision?
I think refusing Sollozo's deal,and let me explain:

The drugs were 'a thing of the future' like said.
Sooner or later Don Corleone knew they had to get into it.Postponding the inevitable is bad financially.Sure,it was not good for political contacts but not taking piece of the action will create a situation where the Corleones will be outsiders to the Cosa Nostra,losing its status as the most powerful family.
The results speak for themselves.Later on,in the meeting of the five families,it is clear that Barzini has won the respect and the status Don Corleon used to have.
Not only that,but in that meeting,Don Corleon agreed almost to the same deal Sollozo was offering.Only now,hes accepting the offer a little too late,after getting shot at..and a long time for recovering, and after the loss of his son,Sonny.
It could have been avoided if he took the offer the first time.
But the worst part of his decision was that he knew the risks,he knew he was risking his family by not taking this deal,and that was not worth it.
- He was waiting to meet Sollozo after Connie's wedding cos he knew there might be problems.
- after giving his answer to Sollozo,he expected problems,thats why he sent Luca Brasi to sniff around.

He had no backup from the other families,that was a poor decision to risk his family and the prestige of the Corleon family among the other families simply to maintain political contacts,in which he didnt get all that much of a profit anyway when he refused to share them with the other families.

What do you think about all that?
and what do you think was his worst decision?(if you do not agree with me)