Think of it this way, the MM do make money off of the spread, and when the stock is weakened by selling, the spread is more is more likely to widen in their favor. By short selling they also cause the weak hands to follow suit. Without that, the MM's job would be harder as the stock pps would tend to stagnate when the momentum ran it's course. In other words, the MM by the shorting gets involved with a certain degree of MANIPULATION. That's just My opinion. It's not unique to this stock as you all know, but without shorting, the PPS IMO would be more stable.