Quote from clearinghouse:
I don't trade the first half hour myself, and I am an automated trader. The opening is too whippy and the slippage is out of control, and you can pay too much with market orders.
I don't blame HFT market makers though. The guys who move the market can do a lot of damage quickly and very fast, and most people are not going to want to be on the receiving end of the abuse, whichever way the markets are going. Somebody's losing on those moves, and they're the worst moves to lose on.