Thank-you for the flattery.
You make (as ever) a very good point, and one that reinforces my central objection, that this is not so much a campaign about raising revenue for any particular issue, or about modifying the behaviour of the markets but about getting back at the nasty bankers.
I always dislike it people criticise celebrities for jumping on bandwagons (even though I did it with my reference to ‘banker/economist Bill Nighy’) because if we restricted opinion or commentary to experts only we wouldn’t be a democracy (or have blogs, though that might not be a bad thing). But this one I really do dislike, no-one really seems to understand even the simplest aspects of it, either the potential benefits or the potential pitfalls and therefore latch on to the marketing message.
As you point out, one of the consequences of tax is to modify behaviour somewhere along the line. I don’t think the tinkering with the VAT rate did much to modify consumer behaviour, but given the lack of price changes on 1 January 2010 I think it did mean that businesses spent the latter part of 2009 adding 2½% to their prices so they could ‘absorb’ the increase for their customers (and hopefully modify customers’ behaviour in January as they took advantage of ‘frozen’ prices). Robin Hood will either change the way the markets work, in which case it will mean a different economy and small tax revenues, or be absorbed as a cost of business. The problem with business costs is that someone, somewhere, will end up paying them.