Vito brands Sonny a 'bad don' but I think Sonny did the best he could, he didnt retaliate the second he heard about the shooting, he waited, he discussed, he found out who the traitor was in his family and had him killed - as Vito would have done, and he took Bruno out in part for trying to off Vito a second time, but also for hitting Luca Brasi...would Vito truly have not responded in kind under those circumstances? A man that one shot a man in the mouth simply because he demanded $200 off him?
It's unclear how much Vito knows of the process that led to Michael's killing of Sollozzo and McCluskey, and it's unclear what makes Vito brand Sonny a "bad Don."
Hovwever, it seems like Sonny's desire to kill Sollozzo is the right move for the wrong reasons. There's no indication that Sonny thinks strategically or looks at the big picutre. He certainly doesn't seem like the type to keep his enemies closer.
Sonny is willing to let business suffer to get revenge and his instinct is to forego a peaceful solution on principle alone.
All in all, I'd say indications are that Sonny was bad Don.
