Well, that's a difficult one. Of all the characters in Shakespeare's canon, I would argue that only Aaron of Titus Andronicus and perhaps Richard III exceed him in patent villainy. If it were put to me to argue this point, I would say that the best option would be to portray him as a symptom of a paranoid, misogynistic and widespread perception that women will inevitably betray their husbands. Look at Leontes in The Winters Tale. He seems to suggest that husbands are all members of a brotherhood of sorts, in which they all share the cuckold's horns and find a kind of solidarity in it. Iago displays a similar kind of sickness of thought. He briefly suggests that he believes his own wife to have been unfaithful with Othello. You could argue that his rage and subsequent malevolent plotting stem from the anxiety that is pervasive in a society of men who are all simultaneously predators and victims. You could also argue that he is railing against a meritocracy that values ability vs. loyalty (which seems to be his argument occasionally). Thus his frustrated ambition is a product of conflicting notions of value. Though this would be fairly weak on its own, it could augment the other argument.