It will take the people on Wall St. about 2 days to stop trading 'shares' and start trading '1 millisecond options'. Firms like Goldman Sachs make money by skirting the laws and regulations. While the average investor would end up paying this tax.
Trader 1 puts in a order to sell everything if the market goes down by 4% in 1 hour.
Trader 2 knows that and wants to get out of the market before trader 1 does in a crash, so he puts in a order to sell everything if the market goes down by 3.9% in 1 hour.
Trader 3, Trader 4, etc. continue this process.
Then you have a day like yesterday when the market goes down by 2 percent and there is a lot of uncertainty about Europe, causing more people to put in stop-loss orders. The one automatic order triggers hundreds more.
Now they are going to rollback some of these trades because it was an "Trading Error". When Investors on Wall St. have trades that make money it is because of their skill and they get bonuses. But when their own stop-loss program sells for a 70% loss they get a do over.