To respond to your comment though,
"The aggregate effect of HFT might change the amount people decide to put on orders, resulting in their buying higher and selling lower."
I'm trying to figure out the linkage. What mechanism would connect the order pricing from a long term investor with the activities of an HFT trader? HFT works in the first and second derivative space of values and long term traders seem solidly in the linear space. Can you construct and example where the activities of an HFT trader are both visible too, and influential on, the pricing targets of a long term investor?
Oh I do have some Bank of America stock (one of the stocks called out in the article) which I bought in 2009 when they were pummeled by the Countrywide fiasco and their inability to get another CEO, sold half of it for a 100% gain, (net 50% gain on the total investment) and have watched the remainder go up and down. I got my 50% return (and that cash is working elsewhere) and I've got some extra shares that I could sell for anything over $0 to add to that gain (although if you want to do the annualized computation it gets lower if I holder it longer etc etc) but holding that since 2009 pretty much defines a 'long' holding.