https://www.nytimes.com/2009/08/03/opinion/03krugman.html
> It’s hard to imagine a better illustration than high-frequency trading. The stock market is supposed to allocate capital to its most productive uses, for example by helping companies with good ideas raise money. But it’s hard to see how traders who place their orders one-thirtieth of a second faster than anyone else do anything to improve that social function.
> What about Mr. Hall? The Times report suggests that he makes money mainly by outsmarting other investors, rather than by directing resources to where they’re needed. Again, it’s hard to see the social value of what he does.
> And there’s a good case that such activities are actually harmful. For example, high-frequency trading probably degrades the stock market’s function, because it’s a kind of tax on investors who lack access to those superfast computers which means that the money Goldman spends on those computers has a negative effect on national wealth.
He was still against HFT, that was part of his point. He was saying that even some of the surge of 1995-2005 might have been an illusion, because it was "only" HFT. If you feel that HFT really does raise the USA standard of living, then of course you are free to view the surge of 1995-2005 as entirely real.
https://krugman.blogs.nytimes.com/2009/11/09/reagan-mythbust...
But that was written in 2009, before it was clear that productivity slowed again after 2005.
In a later post, Krugman analyzed the higher productivity of 1995 to 2005 and shows much of it was simply big box stores and HFT.
In general, the period since 1973 has been disappointing for productivity. And as yet, computers have not brought us the kind of sustained productivity growth that we saw in the early to mid 20th Century.