You said "absolutely nothing wrong".

Regardless of the legality - the entire stock market, is not mechanisms which lead to equitable and socially beneficial distribution of resources, efforts, products, services. Fundamental needs and well-recognized valid interests of the majority of the population (in the US and in the world at large) are unmet and unattended to, while limited interests of small elites are well catered to.

So, there is a lot wrong with short-selling as part of a wider mechanism.