It doesn't. These kinds of actions are entirely competition between HFT firms (the fastest ones get the biggest share of the pie). But the HFT firms as a whole

It doesn't. These kinds of actions are entirely competition between HFT firms (the fastest ones get the biggest share of the pie). But the HFT firms as a whole do provide a service to the market, and at a much lower price than the alternatives, even with the apparently extravagent cost of these efforts (mainly because it requires a lot less people: old-school market making involved a lot of people on trading floors).