The flaw is that an asymmetrical market would develop and one side would dominate. i.e if buyers came in at 117 they may take out 500k of the U seller. If the market didn't then swing back the other way the U bid would be left high and dry. If the U then wanted/needed to recover the 500k of shares sold he'd have to enter the market higher up and book a loss.
For this reason when U's are placed to pressure the market the initiator usually keeps them a tick or two away from the bid/offer as he has no intention of being hit.
