Why is Short Selling of Stocks Needed?

I've heard in various news stories that there was an abnormally high amount of short-selling (i.e., betting that stocks would go down) just before September 11 and backers of the terrorists probably benefited when the market retreated.


Given that another major (e.g. nuclear) terrorist act would almost certainly send the stock market into a deep decline, would restricting short selling be a good idea? Is short-selling a necessary method of allowable investment. Is it time to get rid of it and other similar investments?


Regards,


Rick