I’m concerned with these companies with computer algorithms making trades, when they see unusual activity I’m not convinced that we have a handle on the collective dynamics they might cause...
After watching what computer-controlled "portfolio insurance" did during the Crash of 1987, I was concerned that as computers got faster and faster, and the coaxial cables to the trading floor got fatter and fatter, that we'd someday have gigantic bull and bear markets happening at the rate of several dozen per second. Fortunately, there still seem to be enough inertia in the system that this isn't happening.