Make no mistake; Harry knew Riddle was rotten to his core. He still had nightmares about snake-faced Voldemort torturing him in a graveyard, about charming and handsome diary-Riddle setting a basilisk on him, about Voldemort’s disfigured face screaming at him out the back of Quirrell’s head. Harry had seen Riddle in several forms and they were all evil. That’s just who Riddle was. Riddle being evil was as inevitable as the sun rising, and even if he hadn’t realized his true form as a Dark Lord yet, Harry knew it was coming.