The animosity towards shorts is understandable.
This is where I wonder more and more about the cognitive disconnect people have about bitcoin. There are so many pumpers around here, lamenting short-sellers. In any normal market, we would all be saying "great!" to short-selling; it's responsible for the revelation of true prices in the face of overblown hype (longs being the opposite in terms of excessive pessimism). However, the negative sentiment towards shorting around here tells me that people really do know (or at least feel) the risks of low USD/BTC exchange rates: attack vulnerability, failing exchanges, and massive market manipulations by average people. It's kind of like everyone knows that downward price pressure really increases the risk of full-blown failure, and so the opposite "it will never die, (screw short-sellers!)" mentality has to surface for self-preservation by long-position holders.
I am by no means a skilled trader, but I would assume that the most effective short strategies involve relatively short-term positions, and contribute very little to overall price movement.
Well, you're not totally right on that. Effective short-term shorting requires low volatility, and as instant-as-possible trading. Neither of those exist for BTC. In addition, the most convenient way to short is Bitcoinica, and they are a brokerage, so your activities there are not reflected immediately in the exchanges. They could be aggregating all kinds of movements in whatever direction their hedging algorithm dictates at the moment through many small trades, or single large ones.
With that layer of opacity (and market power) between your trades and the exchanges, it's a difficult argument to say that shorting BTC really is improving fundamental price discovery. Mr. Z can state his intentions all he wants, but the fact is he can act as a market maker at any point.
Again, I think most people at least feel this, if not know it explicitly about bitcoin: falling prices are a serious risk for the sustainability of bitcoin.