For mini crashes, I think an argument can be made about HFT potentially making the stock prices, etc… less normal and more fat-tailed, and thus less well handle

For mini crashes, I think an argument can be made about HFT potentially making the stock prices, etc… less normal and more fat-tailed, and thus less well handled by statistical models (e.g. http://www.bankofengland.co.uk/publications/Documents/speeches/2011/speech509.pdf http://www.bankofengland.co.uk/publications/Documents/speech...). Quantifying how much, of course, is another matter.