In theory you're right, but in practice, it breaks the mechanisms which ensure that investors actually want to participate in the market. The function of the m

In theory you're right, but in practice, it breaks the mechanisms which ensure that investors actually want to participate in the market. The function of the market is not job creation, however one of its functions is to incentivise investors to invest rather than store their money under the mattress. HFT hurts that incentive, that's why it's functionally bad. The purpose of the market is to get all that capital out of the mattresses and into the economy, not to be liquid or efficient. Those are secondary objectives. To get investors' money, it needs first of all to be perceived as fair.