Oh, man, I love, love, love the warped psychology of this...! The reasons he does this, the fact that he knows his own justifications are bullshit, and the sort of dark, spiraling addiction of it all. I especially like the idea of Ron, the youngest boy who got the most hand-me-downs and the least attention, cheating on Hermione because he wants something he doesn't have to share with everyone. Hermione is the sort who "belongs" to the whole world, in a way, isn't she?
You nailed it, as always. ♥