Robin Hood Tax

A nice example from Tim Harford of the risk that Tobin tax increases volatility.

The tax would certainly be attractive if, like a tax on carbon dioxide or congestion, it reduced destructive activities. But would it? James Tobin and John Maynard Keynes both proposed taxes on financial transactions and each believed that the tax would reduce financial volatility. This is possible but far from obvious, when you realise that the tax might encourage bigger, more irregular financial transactions. An analogy: if I have to pay a charge whenever I use a cash machine, I make fewer, larger withdrawals and the amount of money in my wallet fluctuates more widely. Bear in mind, too, that the most bubble-prone asset market is for housing, which is bought in very lumpy, long-term chunks