Situations like this give me the inclination to treat D&D Good™ and Evil™ as physical properties rather than moral tendencies. D&D Good™ that is a little too eager to murder beings labeled as Evil™ falls short of what I would consider good. If someone used such power to kill someone who is a pathological liar and petty thief, that wouldn't seem good to me even if that person could be classified as Evil™ as the system defines it.

Then again while to me such act seems evil, I don't think I could call the caster Evil™ because D&D explicitly endorses killing Evil™ creatures as a Good™ act. Since the 1st edition, the purest paragon of Good™ that is the Paladin wields a weapon to kill.