The price of bananas is generally likely to fluctuate less as a result of shorts, futures etc.

The distinction between investing vs gambling and positives and negatives sounds like more the subject of a PhD thesis than an HN comment! At some point the marginal benefit of smaller price spreads from very short term trade to actually allocating physical capital and labour to producing more valuable stuff might actually be lower than the amount it simply inflates asset prices, but that is much closer to microseconds than "you're not allowed to bet against this IPO, the insiders artificially pumping its value need to be able to cash out first"...