Restrain Evil

If characters such as Iago despise those who have a lack of restraint in their emotions, then they must be suicidal. Iago hates Roderigo because he cannot control his love for Desdemona, and our super villain hates Cassio because he cannot restrain himself with wine. Yet when Iago unleashes his full wrath he is not restraining himself at all. He is taking full pleasure in his game with all of his puppets. So why do villains never look in the mirror at their own behavior. I guess they believe they are restraining themselves to their limit but I think they could moderate themselves a little more rather than go off killing generals.