Ironic because they see (Desdemona) sees tragedy as his heroism and his appeal, the pity she has on him. And yet he only turns more pitiful because he passes more and more tragedies later on. Desdemona is even more of an angel then. Cradling the child of a devil

Is this Shakespeare condemning the unjust nature of women having to take the blame for all -- or an emphasis on her angelic and merciful nature, juxtaposed with Iago's devil persona?

If Iago is reason, and Roderigo seeks reason, and Iago is the cause of all this destruction, then it should be said that the human need for reason (which crushes emotion) is what brings downfall. Logic is what has cut off Othello's motivation (heart). Iago is the personalization of human reason

The fact that Desdemona is sometimes represented as divinity, as a guardian angel, shows that the fact that Othello is rejecting her advocation shows he is falling into his devil, into his inner Iago -- he is losing touch with God, with righteousness (while ironically thinking he is doing the right thing by being civil)