Proposals for a small tax on investment transactions seem to make some sense. Ordinary investors, small or large, are likely to buy or sell a small percentage of their holdings each month or year, while high-frequency traders could turn over theirs dozens of times per day. A tax of, say, 0.1% would hardly be noticed by investors, but could make high-frequency trading (HFT) unworkable. If HFT helps destabilize financial markets, then taxing trades this way would raise some revenue while improving economic stability.
Though I don’t see such a tax as consistent with geoist principles, it seems a lot less damaging than many of the taxes we already face. The problem is that it cannot be enforced. Trades can always be done in some way “off the books,” probably legally but otherwise if necessary. Since those who benefit from HFT also have resources to control relevant regulatory decisions, any such tax will have loopholes or other means to prevent effective enforcement.
most investment banks offer significant UK traders “contracts-for-difference” which are contracts that precisely simulate equity ownership while circumventing UK taxes on transactions (“Stamp Duty”).
— J Doyne Farmer and Spyros Skouras
“An ecological perspective on the future of computer trading” (pdf)
So what to do about HFT? If we consider what HFT deals in, which is largely securities issued by corporations, it may be appropriate to modify the privileges that government grants to corporations, in ways that would make HFT less damaging.