The Thesis of Harry Potter

Ladies and gentlemen, I give you the theme of Harry Potter!  Or, well, one of the many, many themes...anyway!

To love at all is to be vulnerable. Love anything and your heart will be wrung and possibly broken. If you want to make sure of keeping it intact you must give it to no one, not even an animal. Wrap it carefully round with hobbies and little luxuries; avoid all entanglements. Lock it up safe in the casket or coffin of your selfishness. But in that casket, safe, dark, motionless, airless, it will change. It will not be broken; it will become unbreakable, impenetrable, irredeemable. To love is to be vulnerable.― C. S. Lewis, The Four Loves

Do I have proof that this is actually what Rowling had in mind? No, not really...oh, wait!

The Tales of Beedle the Bard:  "The Warlock's Hairy Heart "
Synopsis:  This dark, "gothic" tale tells of a young warlock who removes his own heart by terrible Dark Arts to protect himself from the foolishness of love. When he meets a witch who he wants to win for himself, his folly results in the both of their deaths.

Now, I would have to say that the ultimate thesis is love is stronger than death. But Lewis's quote is certainly another aspect of that overriding theme.