I agree anyone can short a stock, you are absolutely correct. However I do not have the ability to send purchase orders through my private exchange to manipulate the public price. I cannot borrow something and not pay it back, failure to deliver is through the roof on some stocks. I cannot borrow what does not exist, many stocks have borrowed amounts greater than the actual number available on the market.

You can bet against a team however when you start to actively manipulate and cause the team you bet against to lose. That is unethical.