Can't ban negative prices. What happens when locked limit offer at 0 and IB wants to liquidate a customers position?
What if ... the opposite happened. Crude skyrocketed $50, $100 higher on settlement day and shorts were burned. "Everyone" would rejoice. But shoe was on other foot so naturally it must be manipulation by those rotten thieves.
Read the article. This was on expiration when contracts get thinner. You can have thin moments in any very liquid instrument.