We have in evidence a mechanism that allows someone to take a risk with INFINITE liability.
Why do people keep saying that? It's moronic. The short seller's liability is limited to his assets. They're finite. Capitalizing "INFINITE" doesn't make anything in a real economy infinite. If the stock goes up more than the short seller can afford to cover, he goes bankrupt, same as any other borrower who borrows more than he can repay. The lender gets back only a fraction of what she lent, same as any other lender who lends to a deadbeat. It's a risk she chose to take, same as any other lender, period.
Of course, the fact is, it comes from selling something you do not own.
I'm reminded of the last time I had to explain short selling to somebody outraged at people selling something they don't own. This engineer was a recent immigrant from Bulgaria with no understanding of private property beyond what little the communist authorities had allowed their subjects to experience.
"Sell" is just a word that means "trade", applied to trades where what you're receiving is money. To sell something you don't own is no different from trading away anything you don't own; the circumstance that you get money for it instead of something else is immaterial.
So let's say she and I are standing in line at the company cafeteria and she finds herself short of cash. Not wanting to miss lunch, she asks me to lend her five dollars. I do so. She makes her selections and goes to the cash register. Just as she's about to hand over the money to the cashier and get ownership of her sandwich in exchange, suppose I call a halt. "You can't trade away that five dollars! It's not yours! It's mine! It's unethical for you to trade away something you do not own!" You can see how absurd that would be, yes? The whole point of lending her the money was so she could buy lunch with it. I will never see that V-note again, and that's how it's supposed to be.
What makes it unethical to sell a bicycle you don't own but not stock you don't own isn't that you don't own the bike, but that the bike, unlike money and stock, isn't "fungible". It makes a difference which bike you return to the owner. Handing me five ones, or handing me a ten and getting five more ones as change, are every bit as good ways to return my money as handing me my original V-note back; likewise, returning different shares from the ones a short seller borrowed is as legitimate a way to make good on the debt as returning the original shares. Of course there's a risk that the stock will shoot up so much the short seller can't pay his debt; but then there's a risk the Bulgarian lady might get fired and never be able to pay me back the money she owes me.
Shorting is an act that assumes more risk than can ethically be considered acceptable because since no action can be infinitely rewarded no action that ostensibly creates this infinite risk can ethically be allowed. It is a gamble that nobody in the universe can actually guarantee a cover of.

Nobody can guarantee anything in this probabilistic universe but death and taxes.
Thus it is unethical, particularly under the expectations that you do not gamble with other people's money.
Haven't you ever seen a player "go light" in a poker game? There's no such expectation, at least among rational people.
It is, fundamentally, the sale of and profit off of equity you do not own.
It doesn't matter why. It's still. ... Wrong.
I.e., it's against your religion. You speak with the same fervor, certainty, and economic childishness as every medieval true-believer denouncing a Jew for charging interest.
Edit: case in point, the clearinghouse and the hedge fund engaged in unethical and illegal collusion with a number of markets to engage in price setting schemes and forced closure of long positions of others to cover their short positions. It was transparently the motivation to commit crimes to prevent the bankruptcy of many firms that made bad decisions.
That's not at all clear; but if it's true the courts will sort it out in due time. Nobody here is arguing short selling should be unregulated.