This is an idea I like. I'm not expert enough to say it's a good, workable idea, but I like the notion none the less.
I see the justification being that each financial transaction represents a contract of sorts (or may be accompanied by an actual contract) and the tax on that transaction is the price paid to have that contract enforced by law and everything that entails.
I would be very interested to see how they define the word transaction.
For example: Is a private citizen moving $250 from their checking act. to their savings act. a transaction?