I'm no economics whiz, but as it was mentioned earlier...the goal isn't necessarily to increase revenue, it seems to be more along the lines of getting rid of all the small guys.
When you get rid of all the small guys and liquidity, prices are much much easier to manipulate.
May not be the only reason they are wanting this tax, but if the gummint's goal really is socialism and total control...getting rid of the free market is high on the to-do list.
Liquidity offers built in checks and balances to prices...when you get rid of it....the gummint, goldman, et al can make prices what they want them to be.
Just look at how prices get manipulated in thin after hours/holiday markets...it would be the same concept only on a permanent basis.
Just think- next time oil (or whatever the commodity du jour is) skyrockets, instead of blaming speculators, we can say it's some other country holding us hostage with oil prices and start launching missiles, etc.