I get paid each fortnight, so once a fortnight I update my finances, log on to the share market and buy my next intended parcel of shares.
From my point of view, I probably am better off with HFTing existing, because when I want to buy a stock, I assume it means that it will be available for me, and with less of a spread, then would otherwise be the case.
Maybe, (I'm just looking at a stock now on the Australian exchange (NAB if anyone cares), its buy/sell spread is 26.14/26.17, so let's say at worse HFTing means I pay 0.03/26.14 = 0.11% more than I should ... who cares, after 2 years, that'll lower my average profit per year by 0.05%, in 10 years by 0.01%, and of course, it matters less and less the more, and more years I hold it for.
Now I understand that people who try to do buy-and-sell strategies would care more about this than a buy-and-hold person, but either the buy-and-sell person is
a) one of the few god-like people who can beat the stock market - in which case, they really shouldn't care about this, or
b) their part of the great mass of people who would be better off buying index funds - in which case, just buy an index fund!