PROFIT IS THE ONLY THING ... but HFT does not support that, it supports bleeding out value that the system would like to bank, and it changes the dynamics of trading from "is this a good firm to invest in" to "is there a greater fool out there for me to sell to tomorrow (or in 3 seconds)". The first question serves the market system by making viability and good practice part of the business model while the latter simply tries to skim the tops of the bumps in a way that distorts the markets. The politicians who get this are the one who would be pushing back against HFT with every tool they can, including a microtax. The ones who don't, well, don't blame me, I didn't vote for them. And a 0.03% microtax collected hundreds of times a day on a single trader is completely sufficient to change the equation for a computer model that is trying for .02% return on each trade, but won't make traders working on fundamentals even blink, since they are trying for 10% on a long term dividends and growth basis.