[Mikeb85]

There are limits to algorithms. Stock prices are affected by human behaviour, which can't always be predicted.

Not to mention the various macro variables, like wars, weather, crime, etc... Plus, what time frame should the algorithms trade on? They're very good for predicting the very short term, I haven't seen much evidence that they're good for predicting longer time spans.

While algos eat up arbitrage and electronic brokers replace human ones, humans are still very good at other forms of trading... Not to mention, a large part of market activity isn't even trading - it's long term investing and collecting dividends.