We're uncontrollably worked up over Harry Potter and the Deathly Hallows, and all month we'll surf the Potter fan sites, scan the message boards, and read the tie-in books to argue the biggest pre-publication speculative debates.
Theory: Despite the fact that he killed Dumbledore, Severus Snape is still working on the side of right.
The argument for: In short, Dumbledore trusted Snape, and so should we. The moment of the headmaster's death has been endlessly hashed over, but something seems to have passed between Dumbledore and his Potions master before Snape cast the Avada Kadavra spell. Dumbledore plead with Snape: "Severus, please…" Was he pleading with Snape to kill him so that Draco Malfoy will not be a murderer, or murdered? Perhaps the potion he drank back in the cave would kill him soon enough? Also, J.K. Rowling has dropped hints that there is more to Snape than meets the eye and that whether he is good or bad will be of dramatic importance as the story plays out. Would she have said that if we were meant to accept the obvious conclusion, that Snape was evil?
The argument against: What argument? He's a greasy git who killed Albus Dumbledore. He's always been a Death Eater and always will be.
Our take: J.K. Rowling has made it clear that the moral of the story, as it were, is that love and trust are stronger powers than hatred and deception. If Dumbledore was wrong about Snape, it invalidates the moral. Snape will be redeemed and will die the hero he always wanted to be.
Wade into the debate: This is the most hotly debated question in the Harry Potter world. Gigabytes of message-board posts have argued the point, but the best way to dive into the Snape situation is to read The Great Snape Debate by Amy Berner, Orson Scott Card, and Joyce Millman, an exhaustive, unauthorized paperback specially published by Borders. We read it on the beach during our nerdcation!