Quote from ProfitTakgFool:
I'm not 100% sure of this -- I just trade the darn things -- but if they banned short selling on futures wouldn't the open interest trend to zero?
For example, you buy a contract and later sell it to another buyer -- open interest stays the same. All that happened is the contract changes hands. If a new buyer comes into the market and buys the contract from a short seller both parties are creating a new contract and open interest increases.
If you can't sell short the futures you can only sell a contract you purchased earlier so therefore, at the least, open interest could never increase but only decline as contracts are offset. Open interest would eventually go to zero and the futures market would cease to exist.
You are exactly right. Any zero-sum market cannot exist without short-sellers.