Can high-frequency traders replace active investors in an ideal world. Ideally, the price should be the best estimate of the value of the company based on all publicly available information. When new information is released, high frequency traders should rush to profit from the discrepancy. Further, they can market make based off their knowledge of the stock's true value. However, this business should face increasing competition until it becomes a low-margin business. I don't see any inherent reason, active investing should be super profitable. In the end, it is just another business like any other.