As others point out, short-selling is just another way to pursue Buy Low Sell High … except that the temporal sequence is reversed! There’s huge short interest in many NYSE stocks. I hope one of the SDMB stock trading experts will comment on the scale of these massive short interests, and what their side effects are.
Non-“casino” sorts of shorting are possible. For example IIRC, Helena Rubinstein shorted a large number of shares of her own company, Rubinstein. She didn’t short “against the box” (i.e. turn her own shares over to her broker as collateral, so the sale could proceed) but rather borrowed them from a relative. IIRC the purpose of this was to avoid capital gains tax that result from an ordinary sale. (If the intent is to cover soon, this seems not unreasonable and AFAIK may even still be allowed by IRS in well-defined cases.)
As practical advice for amateur investors (such as myself) it’s important to note that the smallest and largest players are very different in what they can do.
A big player might short 5 million shares of AAPL naked, receiving $580 million dollars. He’d have to pay out the 2% dividend to the stockholders whose shares he borrowed, but would be out only 1% net, if the broker paid him 1% on his cash balance. (This is clearly reasonable; if you borrowed to buy, your dividends would help offset your cash interest payments. Though retaining control of your cash for collateral, the broker will certainly be putting it to work.)
A little player would not receive interest (excepting a few generous brokers) on the cash (a huge difference unless interest rates are very low), nor would he be allowed to short naked. (Regulations have tightened; is naked selling still going on?) Because of these and other disadvantages, I think small customers who want to gamble are better advised to buy puts. Experts?
The question is unclear. Are you asking why people like to gamble? Or whether short selling serves a public interest?
In its purest forms, short selling is a “natural” act which it would over-authoritarian to ban. And most of us agree that serving the public interest is unnecessary for any mechanism, as long as it does no public harm. (Companies whose shares are shorted sometimes complain that it harms them, but is that harmful to the public? Some would argue, I think, that in those cases the shorters may be serving the public interest, by discouraging investment in an overvalued firm.)
There are stock trading practices which do pose risks to the public, and should be regulated or taxed. But short sales wouldn’t even make the (well) short list of such objectionable practices.