There has been relative gain by a very important class of investors: individual retail investors. If you trade individual stocks for your own account, you've seen a steady decrease in the amount of spread that you have to pay to get your order executed and you certainly shouldn't be deluding yourself by thinking that you are competing with high frequency/low latency traders or that they will be somehow disadvantaging your orders. The people who are at the root of these complaints are the buy side institutions who don't want to invest in technology to improve their order placement and the older exchanges who are either also trying to avoid investment or who are struggling to protect obsolete business models. If the various proposals to limit the rate of trading are enacted, then spreads will widen out even for the large buy side players (perhaps even by an amount larger than what HFT is currently costing them), and the only winners will be the entities that want to remain fat, dumb, and happily protected by regulators.
I just realized that I had a wrong idea about how HFT works. Though I am still not sure about how the pros and cons add up, your comment convinced me that it is more complicated than I thought.
HFT is a disruptive technology that has been the target of lots of FUD from entrenched institutions and politicians looking for a "scary" issue to flog. Most of the practitioners are fairly small (relative to other investment firms) and technology-focused. Unlike complex, bespoke derivatives and products such as CDOs, this aspect of the markets is fairly well regulated, with a focus on bringing transparency to pricing for individual investors, which is in stark contrast to the regulatory environment in Europe and Asia.
