Proponents of a transactions tax misunderstand the way markets work. The bubble in home prices in the United States was not caused by the rapid buying and selling of individual family homes. The financial crisis was primarily a liquidity crisis and a credit crunch, and the major problem with collateralized mortgage-backed bonds was that they declined significantly in value and became illiquid. A transactions tax that would have reduced trading and made repurchase agreements more costly, could have made the problem even worse.
Moreover, "Wall Street" would not foot the bill for the presumed $150 billion tax. In fact, the tax would simply be added to the cost of doing business, burdening all investors, including 401(k) plans, IRAs and mutual funds. ...
Transactions costs have declined significantly over the past 10 years, thanks to the many structural changes in equity markets, including trading in decimals instead of eighths, the proliferation of scores of trading venues that function as exchanges, and an explosion of high-frequency trading. Vanguard has estimated that total transactions costs on an average trade have fallen by more than 50%, resulting in approximately $1 billion of annual savings to its investors. When magnified across the whole investment industry, investors have probably saved tens of billions of dollars in transactions costs.
Transactions taxes would make most current high-frequency trades unprofitable since they depend on the thinnest of profit margins. Trading volume would collapse, and there would be a dramatic shortfall in the tax dollars actually collected by the government. Market liquidity would decline, bid-offer spreads would widen, and all investors would pay significantly higher costs on their trades.