A Transaction Tax Would Hurt All Investors - WSJ.com

Often mischaracterized as speculators, high-frequency traders scour markets for minor mispricings and arbitrage trading opportunities. They buy and sell stocks in an instant, hoping to earn pennies on a trade. Far from destabilizing or creating volatility in the market, their actions significantly increase trading volume, reduce spreads, promote price-discovery, and ultimately reduce transactions costs for long-term investors. Such trades might not be doing God's work, but they are socially useful.