Quirrell had older students beat up Voldemort's enemy during class. He squashed a reporter who mildly annoyed him, cast the Killing Curse at an Auror and probably arranged to put Hermione in danger of Azkaban.

Now if Voldemort were supposed to be stupid, this would still represent a change. But all of his most competent opponents say the opposite, that he seemed frighteningly intelligent. And all the old instances of violence, IIRC, served a forward-thinking purpose in addition to hurting people. (At least if you accept my interpretation of the way he treated Bella.)