Clearly, Othello is guilty of misplaced trust--he believes a man whom he didn't feel was fit for the lieutenancy over his wife, and as you note, many factors contribute to the tragedy of the play. Ultimately, though, Othello is responsible for his own actions--and is therefore at fault.
While Othello does exercise poor judgment in whom to believe (especially for an experienced military leader), I think that he--more than any other Shakespearean tragic hero--deserves less blame for his downfall. He is a product of a prejudiced society, a society which uses him for his military prowess and exotic culture but then stereotypes him as animalistic, lustful, jealous, and violent.
Iago knows that Othello is insecure in his relationship with Desdemona because of the difference in their race, age, and social class, and he uses that insecurity against the general. Thus, I think that someone could validly argue that had it not been for stereotyping, Othello might not have fallen as he did.
No, Othello does not create his own downfall. But Iago targets Othello's vulnerabilties. Othello expresses his inadequacy in speech; he compares himself to Cassio and…