Those HFT traders profit from the clumsier pension funds and other similar funds. e.g. algorithm detecting a broker, on behalf of a fund, is buying some stock with one batch per hour, so front run them. They are profiting from teachers and the elderly. I suppose at the end of the day half of the resources lost to those two groups are given to the even more worse off, albeit giving charity administrators a cut.
Fund managers also employ dealers who very much do not buy stock one batch an hour so as to allow HFTs to profit from them. They have a fiduciary duty to their clients to aim for best execution, so if they were being disadvantaged they would be crying out to regulators - who like to look after pension funds.
The head of Vanguard is on the record saying that his firm benefits from HFTs actions on the market. Narrower margins are a good thing.
