While there are some reasons why a failure to act collectively to impose a financial transactions tax might have some adverse consequences, it is pretty clear that imposing a transaction tax would improve the financial markets which are currently too highly affected by algorithmic and high frequency trading. Please take a look at the SEC's report on the flash crash of 2010, (http://www.sec.gov/news/studies/2010/marketevents-report.pdf) especially the pages on High Frequency Trading. The flash crash was caused by the interaction of a large trade overwhelming the market and algorithmic trading systems. A financial transaction tax would make the HFT un-economic -- while the tax would be minimal on any single trade, the algorithmic high speed 'arbitrage' trades would quickly go away since the taxes would be higher than the returns to the HFTs. "For the 6-business-day period of May 3 through May 10, these 17 HFT firms averaged 43.8% of total dollar volume on the public quoting markets. Their trading was divided between 51.5% liquidity-taking buys and sells (aggressive trading – generally taking bids and lifting offers) and 48.5% liquidity-providing buys and sells (passive trading – generally posting bids and offers)."