Probably best just to agree to disagree. I see quite a large difference between what Harry did to Carrow and what Bellatrix did to Hermione and Neville's parents and I wouldn't use the same word to describe those actions. Apparently to you, they fall under the same category.
And IMO, Harry is a lot of things, but never a sadist, nor does he have any sadistic tendencies. Imagining someone who has hurt you suffering is a far cry from taking pleasure in and seeking out opportunities to hurt other people. Harry's emotions in the references you mention are complex, IMO, and I would hardly call them examples of sadistic behavior. By your definition, Severus Snape and Draco Malfoy are sadists (or have sadistic moments) and both are extremely callous to those they consider the enemy. Draco actually talks about Mudbloods dying and seems quite taken with the idea.