Pham Neutra is asking in one of his blog post what's so outstanding about Second Life that so many people are criticizing it right now. He only knows one another thing where the discussion about it is equally emotionally heated - nuclear plants.
Well, so why are so many people criticizing it? Because it's new, it's hip to criticize it, they don't have a clue. Just take a look at earlier things like Rock'n'Roll, Skateboards, whatever - when they first became mainstream, many criticized them, there's a thick, red line of such debates in history. Period.