So, last month,
Canisdoofus and I went to The Witching Hour symposium in Salem. And while I didn't think much of most of the presentations I saw, there was one idea that I really liked: the fact that Snape's mother's maiden name was Prince--and his apparent eagerness to adopt her name as his own--indicates the nobility inherent in his character; Snape is both a Prince and a prince (of a person).
Naturally I loved this idea. However, I was just rifling through a bit of Machiavelli for my own personal interest, and it occured to me: 'The Prince.' You know, 'the end justifies the means.' What if this is what JKR is implying instead? After all, Snape *is* Machiavelli's Prince in some ways; the events of HBP prove this: he kills Albus--with Albus' consent, of course--because both of them know that this is something that must happen to bring them to the end that they need. I'm no Machiavelli expert, of course--in fact, it's been years since I've read 'The Prince,' but this seems much more plausible to me (or at least as plausible) as the explanation given at The Witching Hour.
I feel an essay coming on--I may have to delve back into my world literature anthology and investigate this idea further...