Am I supposed to be appalled by this girl?  MC was going to let a poisoned water source continue to make ill and kill innocent people if Setsuna didn't tell him to cure it.  MC burned alive 10 guards who as far as we know had nothing to do with his previous suffering.  He treats the girls around him as disposable objects to be thrown away as soon as he's bored of them.
Norn in comparison is a sadist with a human pet who seems more than willing in his position, and is being shown as a military strategist who wants to avoid unnecessary losses by weakening the enemy's forces through unethical means.  If this was an attempt to make MC seem comparably "good" this isn't a very good attempt at it.