Robbing who?

The call for a Robin Hood tax—a tax on financial transactions—is not as "anti-capitalist", as some seem to think. It involves calling people not to denounce capitalist exploitation, but to demand a minimal tax on the financial transactions in which capitalists try to swindle each other out of the proceeds of their past exploitation of the working class.

It really is one of the most pathetic reform proposals for which people have ever been called upon to demonstrate for. They want is to retain the world market economy but to try to control it for the benefit of humanity, to humanise it. Their hearts may be in the right place but this is to display an incredible lack of vision as well as an appalling ignorance of the way capitalism works, and has to work.
If just one major financial centre were free of the tax, the currency and financial trade would gravitate there, the financial sector could formally switch its business to offshore branches from the Cayman Islands to Singapore and so undermine the intended restricting effect. Failure is therefore 'programmed into' such a tax on currency transactions.