"When you're selling something you don't own you're distorting the market's price discovery mechanisms."
How? It only does so if one sets out to do it on purpose, and in that case there is no difference between selling something that own, or that you don't (yet) own.
Let's say I sell grain to you for 300 USD per ton, to be delivered in Fall 2012. How does that distort the market? Alternatively, how is this example different from naked selling? Or isn't it, and do you think that this sort of insurances should be prohibited too?
"In many contexts I think most people would consider it fraudulent to sell something before you've bought it."
I'm not sure. There are many retailers who only order something from their wholesaler or manufacturer after you've bought it from them. Why would a buyer be concerned with when or how a seller gets his merchandise? It only becomes a problem after failing to deliver the goods, and when no adequate compensation for such a failure can be given (i.e., a seller going bankrupt because of a naked sale gone wrong). Something that could be controlled, regulated or mitigated in many ways that are much less intrusive than forbidding 'naked shorts'.