Carrow has used the Cruciatus on defenseless students (people he has authority over) because he wants to intimidate them or punish them and because he likes hurting people. Harry is nothing like that.
I guess we do have different defintions of torture. Obviously Carrow suffered less than Neville's parents, and somewhat less than Hermione. But the spell is incredibly painful, even cast once; using it will get you sent to Azkaban for life; and most importantly, the purpose is to cause pain. If someone causes you pain for the simple purpose of causing you pain - particularly pain that makes you "howl", "writhe" and "scream" - I think you've been tortured. The etymology of the spell shows JKR meant it to be a torturing spell.

Harry does like feeling powerful, though, and has definite sadistic moments, as well as being extremely callous to those he considers the enemy. (See: knowing Draco was listening for him, frightened, in the RoR in HBP gave him 'a most agreeable sense of power'; after seeing the spider tortured by Moody, he imagined doing it to Snape; he was amused to see Marietta Edgecombe wearing a balaclava six months after being cursed with 'SNEAK' across her face, suggesting it's permanent). I find it hard to see his cursing of Carrow as anything but punishment for spitting in McGonagall's face.