First off let me say that i didnt like Roth but i understood his motivation it wasnt like he was like Barzini who just wanted to have it all. I think Roth realized how utterly ruthless and cold blooded mike was and thats why he wanted to get rid of him. Now im not saying Roth wasnt ruthless he definetly was but not as bad as mike. He obviously respected vito so its not like he would turn on anyone like barzini did