You say: "Tom tended to protect the weaker students." Could you please give me an example, from the text? I can, for example, cite a dozen instances of Snape acting protectively. I cannot think of one single example of Tom doing anything positive for anyone weaker than himself, unless he had something to gain from it. As Greenwoodside said in her essay, Rowling has written him (Tom) as completely immoral from an early age. We may not like it, but that is what she has done.