"Then what are you?" A beat. "Please do not say 'a monster' because that is inaccurate beyond my ability to ignore."

They have, in this past mission, done monstrous things. Become monstrous things. But it cannot possibly be their fault for failing and falling- if it were some flaw in his system that led him to this? Cortana would have torn him apart line by line.

She had not.

Therefore: something else was at play and while they are not wholly innocent, neither are they wholly guilty.