This is an interesting perspective, and indeed there are key characters whose voices if the were heard, could have averted some of the tragic events of teh play.
Desdemona is given a voice at the beginning when Othello asks her to testify as to the origins of their relationship. However, Othello ignores her protestations of innocence regading his suspicions of her affair with Cassio and kills her anyway. Emilia is killed by her husband when she reveals Iago's evil plan, and Bianca is cast aside and abused, becoming part of Iago's plot to frame Cassio.