It's rewarding to be "short" the market during a rapid decline, but no one should assume that it's easy to do so. You still must overcome the challenges that accompany any stock trade: The right entry and exit levels, the appropriate vehicle, and (most importantly) the discipline to follow your method.
Yes, prices usually do fall faster than they rise, so it's obviously true that being on the right side of a downtrend can make for a big win. But this cuts both ways: A fast market affords less time to think about what you're doing.
When real panic sets in, the issue becomes whether short selling is even possible. As the markets went into free fall during September 2008, the SEC imposed a temporary ban on short selling. More recently, European financial authorities imposed a short selling ban on European bank shares.
So there's every reason to think that the government will do likewise next time -- especially if the larger economy itself is in a general deflationary spiral.
Short sellers are made out to be the "bad guys" who are driving down prices during a panic, but you might be surprised to learn who is really doing most of the "driving " when fear is in control. Here's an excerpt from Bob Prechter's Conquer the Crash:
"In a bear market, bullish investors always come to believe that short sellers are 'driving the market down,' when in fact, the decline is almost entirely due to selling from within their own over-invested ranks. Sometimes authorities outlaw short selling. In doing so, they remove the one class of investors that must buy. Every short sale (except when stocks go to zero) must be covered, i.e., the stock or derivative contract must be purchased to close the trade. A ban on short selling creates a market with no latent buying power at all, making it even less liquid than it was.... Like all other bans on free exchange, a ban on short selling hurts those whom it is designed to help."
All of this duly noted, it is true that so long as short selling in a major downtrend is allowed, the opportunity will be real indeed for investors who can manage the risk. Just beware of two facts:
1) Some brokerage firms may not survive a deflationary depression, and 2) A short position comes with considerable risk.
Are we approaching that time?