Don't get me wrong. I think LotR is much better literature and it is much more spiritually challenging than HP (which is mindless entertainment). However the lines between good (Dumbledore) and evil (Voldemort) are extremely sharp. Voldemort kills many people and for no reason, tortures others (including children). Very sharp distinction.
Just something to chew on. I'm not going to come back & answer anything (or make any new arguments). FWIW, I wouldn't let my child read either HP or LotR until they were in middle school.
Yes, greed tends to destroy itself. It was the good in Bilbo, and later Frodo, that kept them from killing Gollum. That Frodo faltered at the end does not obscure good and evil, IMO.