Just a couple of pointers to more commentary on shorting. The IMA's response to the FSA consultation, and an EDHEC paper on the impact of bans (you'll need to register to get this one, it's the third paper down in this list).
Let's be absolutely clear about this - the overwhelming consensus of opinion is that shorting bans are ineffective (if not actively damaging to financial markets). There is actually a stack of academic evidence that such opinions are based upon. Much as I am sceptical about the benefits of shorting, I really don't see any compelling case against it (except the more general point about trading costs). In short (ho hum) I don't think it is really something lefties need to worry about, unless part of a wider push to reduce stock turnover.