I don't think I get your point. Correct me if I'm wrong but it seems to be that you're suggesting that if I want to sell some of my shares, for example, that I

I don't think I get your point. Correct me if I'm wrong but it seems to be that you're suggesting that if I want to sell some of my shares, for example, that I should wait until volatility is low? If I had a way of knowing when the market would have low volatility, I'd throw away the shares and become a billionaire trading options. Saying you should wait for low volatility before trading is equivalent to saying you should wait until the price is high before selling. Both statements seem to reflect common sense but neither piece of advice can be translated into an actual strategy. The impact of HFT market making isn't that difficult to observe - all markets which have attracted such participants have seen huge falls in spreads. The spread is a tax on everyone who buys and sells in the market so lower spreads are good for everyone. (For example the cost of buying and selling a DAX future before fees was about 70 euro just 15 years ago while the spread is now typically less than a euro.)