When markets get all wonky like yesterday, it makes perfect sense that liquidity is going to disappear. When Accenture for example is rightly prices about $40, but all hell broke loose so I see it trading at a penny. If I can be sure trades will be enforced, I will be happy to buy it at a penny. But the next guy will say "I'll buy it for a nickel" so I better bid a dime, then right on up to price discovery. If I have to worry about trades getting busted, far better for me to reduce my risk and withdraw from the market completely. Too much of a gamble for me to buy at $20 and sell at $30 as I try to add liquidity to the market, if I have to worry that the $20 buy will be busted but not the $30 sell. I would wind up short at $30 when the market resumed normal pricing at $40. When they fool around with the system, that's when things really go awry.