I think this assumes that the principal behavior the tax is designed to change is all at the consumer level. I am not sure that's 100% correct.
Considering that we are all individually and corporately (at an industry level) consumers and producers of CO2 I don't see what you are objecting to especially considering this statement that you also make:
Government AND Opposition. They both have the same CO2 reduction targets. (5% less than 2000 levels by 2020 I think).
I see that you haven't bothered to comment on whether a miniscule change in our 1.5% global contribution WILL actually measurably impact the climate change models...