I agree with the above post that Othello's outsider status is a factor in his downfall. Yet, I also believe that other factors contribute to his downfall as well. One of these is man's inability to view women without suspicion and jealousy. It is the idea of ownership that prevails in the way men view women. We see this idea early on when Iago tells Brabantio that he has been robbed. Brabantio feels as if his daughter has been stolen from him when she eloped with Othello.
Throughout the play Desdemona is referred to as a treasure or a jewel. Roderigo thinks that he can buy Desdemona if he only puts "money in his purse." Cassio praises her as the "riches of the ship." Even though Othello loves Desdemona dearly, this tendency of men to want control and to fear losing it runs deep within him. "We can call these delicate creatures ours, but not their appetites," Othello rages.
It is easier for a man to trust another man who has served beside him in battle than it is for him to trust a woman who married him. If she "can deceive her father," she can deceive her husband, Othello grows to believe. Shakespeare examines the weaknesses of such generalities.
Women are not exempt from these stereotypes either. Emilia exclaims, "These men, these men," exasperated at the way men treat women. "Men are all but stomachs, and we all but food, and when they are through with us, they belch us," Emilia generalizes.
Of course, both stereotypes are faulty generalizations, but it is Othello's faulty perceptions of women that prove most dangerous because he has the power and the will to act upon his beliefs. He actually feels that he is helping the male sex by, in his mind, executing Desdemona. "It is the cause," he reminds himself. "She must die, else she will betray more men," he declares.
In the end, Othello recognizes that he "threw the dearest pearl away." He knows that he did not fully appreciate Desdemona's value as a person. He suffers because he believed that the fair sex was inferior, not capable of great loyalty, and therefore guilty in military terms of treason.
You will wind up with different reads on this. For my bet, part of why I think this drama is one of Shakespeare's most underrated is because it reflects the challenges of being an outsider. I think that this helps to feed Othello's tragic flaw of insecurity and his downfall. Being a person of color, a military leader in a setting of the politically established, and falling in love with a woman who is of this elite status all help to contribute to Othello's feelings of insecurity about who he is and whether or not he "belongs" in such a configuration. The idea that one can fully overcome their outsider status with good works and deeds is put on its head in this setting. Othello's insecurity about who he is in such a social design is where Iago strikes. It works well because Othello's inability to reign in his own self- doubt and perpetual insecurity in both political and emotional realms is what leads him down the path of personal and political destruction.