Short-selling is a way to profit off of a company's fall. It sounds morally wrong, but it also allows someone to put their money where their mouth is and gamble on a company's loss, with the risk being that they lose money if the company ends up succeeding.
Of course, it creates a perverse incentive. A short-seller who is invested in a company's failure will spew tons of FUD around the company, whether it's true or not. TSLA used to be one of the most shorted companies on the market, and many bloggers that were highly critical of Tesla were short-sellers, and the noise it created made it difficult to figure out how bad the problems were.
> Seems like a way to gamble legally in all 50 states.
You could say the exact same about long positions, which is nothing more than gambling on the success of a company, the same way a short is a gamble on the failure.