[A1kmm]

I think there is some truth in that. Markets in which HF trading occur are extremely efficient in the short term, but the information they act on in the short term is primarily about trading and not information which should affect the long term value of the stock.

The Efficient Market Hypothesis seems to break down over the long term when the market is efficient in the short-term, because bubbles can easily develop - and so genuine pricing information gets diluted by complex emergent effects, destabilising the market (in crop futures markets, for example, this has lead to artificial food shortages, and it probably played a role in the Financial Crisis).

I think a transaction tax is the best way to reduce excess short-term market efficiency; if you have to pay the government a small percentage of each trade, people will trade less frequently and only on better quality information.