Because it's putting someone on a pedestal to notice their good qualities. Even when you're seeing them.

[There's confusion in his voice. Noh's talking about putting a part of himself aside and Garrus doesn't know where that can lead that's possibly good. The question only adds to how much Garrus is at a loss.]

And I figure this is going to trouble anyone with a conscience. Not enough to make them stop, because the weight on the other end of the scales is pretty damn high, but we're going to have to kill every man, woman, and child on that planet.

[The confusion fades, to be replaced by a little frustration. Garrus hates what they'll have to do. But there is literally no choice in the matter.]

Green especially, if Ajna is anything to go by.