The economy is, thankfully, not a zero sum game. The profits the Pennsylvania Railroad 'took' from the Erie Canal shipper also allowed a cheaper and more flexible transport of goods for, say, a steel manufacturer in Pittsburg or a salt producer in Syracuse. The bulk of the IT industry is dedicated to making old processes more efficient, and therefore 'taking' profits from some middleman.

The HFT's profits do come from a large mutual fund, but then that large mutual fund can lower it's risk because it can quickly move from one position to another because it can expect a HFT to buy whatever it is selling. Risk has a price (ask an insurance company) and reducing it adds value to the economy.

Perhaps HFT was very lucrative for a while, but competition has naturally squeezed the margins out, but the markets has all the benefits of having HFT around.