Apparently the people doing it are gaining something from it, else as you note there would be less of it. I don't know whether it's value-creating or not as a whole; there are different types and classes of HFT operations and algorithms (including those that try to trade based on rumors and sentiment), and various arguments about who is or is not better off for their existence. Someone who wants to assert that it's harmful needs to have some kind of tally of all the benefits/profits and all the harm/losses that shows net value destruction, or at the very least a complete ethical argument. All we got was "the world needs less of this", which doesn't really do much to further anyone's understanding nor provide a digestible view on the matter.
