Serious question, why is short selling allowed?

I think we have to take the question and flip it, as the law (mostly) lays out what you can't do, rather than what you can. If I own X shares in company Y, why can't I enter in to a contract with you whereby you take my X shares and return them to me on date Z?

If I can do that, why can't you sell those shares and buy them back (presuming I'm okay with that)?

It is just sort of the default position, and stems more from our property rights than anything inherent in securities law.

Short selling is a really useful tool.

Say the price of potatoes is $100 per pound today, but my potatoes aren't ready until next week. Well, I can take out a short contract to lock in the price and when my potatoes are ready I sell the potatoes and close the short.

I'm covered in both cases. If the price goes down I will make profit on my short contract but less price on the potatoes. If the price goes up then my short will lose some value but the increase in my potatoes will cover the losses. In either case I will have gain the $100 I was expecting.

To prevent the market from thinking that a company worth $0 is worth $4 billion

Short selling gives additional financial incentive to research companies and figure out which ones are full of it. That's useful to the market overall, not just to the short-sellers themselves.

I don’t have anything against shorting – still a very interesting question!

Look for wirecard