so, you have to question the true valuation of the markets now. >> kroft: larry leibowitz of the nework stock exchange says there is absolutely no evidence that small investors are being hurt by high frequency trading. most of them, he says, don't care about pennies when they are buying and selling stocks, and they're in it for the longer haul. >> leibowitz: look, there's always been charges for as long as trading has existed that people are front-running orders, manipulating stocks. this is nothing new. i think now you add to it the element of... the mysterious element of the computer, and it makes people even more mistrustful. >> kroft: leibowitz and other proponents of high-frequency, high-speed computer trading say it has performed a valuable function-- tripling volume, reducing stock spreads and transaction costs, and providing liquidity to the markets. >> narang: liquidity means that, if you want to buy or sell a stock, you could do it right away and you could do it at a fair price. that's what liquidity means, and without short-term traders, there is no liquidity. >> kroft: tr