As a believer in free markets, I think it is both useless and harmful to constrict computerized trading. But on days like today, it really puts that belief to the test.
The purpose of a stock market is to provide an orderly and efficient market for the free exchange of equity securities. At the core of the market, there must be a belief that the market is trustworthy, that it can match buyers and sellers, bids and asks.
Today’s market was neither orderly nor efficient nor trustworthy. It was just a bunch of computers making ugly, messy love with each other . And your money hung in the balance.