There is no "sharing community." There are apparently tens of millions of individuals who are active users of these Kazaa-type things. As the price drops from $17 toward zero, we would expect to see a bell-shaped curve describing how many people so far have dropped off Kazaa and moved to a paying service. Somewhere on that curve is the profit-maximizing price. It's not zero, and it's not $17. I don't know where it is. Thievery has not gone to zero at that point, but we don't care: it's the profit-maximizing price, whatever it turns out to be.
The declaration of a class "File Sharers" who have the property "they steal things" and the creation of an imaginary 'sharing community' are both rhetorical devices that group huge numbers of people for the purpose of demonizing them. There is no 'community' that acts in concert, and ascribing a generalized propensity to steal to users of file-sharing programs has a high probability of being a false assertion.
I don't follow this stuff in detail, but I had the impression that iTunes was still Apple-only. We can't tell anything about how that model will affect the entire industry if only ~10% of the people can even get on it. Didn't I read that they've already sold several million songs? It's not like there's no file-sharing software for Apple, so obviously a significant number of people are choosing to pay for something they could get for free. I would expect that; my underlying belief is that most people would prefer to be honest. (Another underlying belief is that people who assume that everyone is a thief are themselves thieves.)
I have the same belief.