I have also thought taxing financial transactions sound very interesting, for two reasons:

1. The rich cannot easily escape it.

2. It reduces incentives to do speculation.

The latter is important I think. Too much trade and financial transaction today serve no other purpose than high speed speculation. By taxing transactions one might be able to encourage more long term thinking. Perhaps we could cut down on wasteful robot trading.

In my a financial system exist to channel resoures to business that needs resources to spend their services and production.

But today the financial sector seems to have just turned into a big Casino for people with lots of money. It is a mockery of the idea of what a finance sector is supposed to do.