Throughout the play Othello, we see an underlying theme of male's distrust of females.  Brabantio, for instance, is immediately incensed that his daughter eloped with a black man.  He does not trust his daughter's judgment.  He immediately disowns her, and declares that he has lost his "jewel."  This type of objectification of women occurs with Iago as well.  He calls women--even the best of women--no better than nursemaids or housekeepers.  Iago has no respect for his wife Emilia and believes that she is sleeping with both Othello and Cassio.  Even Cassio shows some of these same views of women.  For him, women are either put on pedestals to be worshiped, as he does Desdemona, or they are prostitutes, such as Bianca.

These views of women are also apparent in Othello.  One of the reasons Othello is so susceptible to Iago's machinations is the belief that "these delicate creatures (women)" have sexual appetites that cannot be controlled.  Iago informs Othello that Venetian women know well how to deceive a man.  And Othello believes that being a cuckold is a fate that great men, as well as ordinary men, must inevitably suffer.

But having a cheating wife, no matter how common, is still a blow to one's manhood.  It is Othello's pride that is most hurt when he believes that Desdemona is cheating on him:

But, alas, to make me

A fixed figure for the time of scorn

To point his slow unmoving finger at!

By Act 5, Othello feels that he must kill Desdemona out of a sense of justice and honor.  He feels that if he does not kill her, she will betray more men.  Her death is a just punishment, he believes, for her transgression, and he has to remind himself that he is executing her for "the cause," and not out of anger.