[dragonwriter]

> We could artificially create demand by jacking up the price of petrol, but then we are taking choice away from the consumer.

Jacking up the price of petrol doesn't take away choice. It may be internalizing the massive externalities associated with the use of petroleum based fuels and making the choice better reflect net utilities (including disutilities experienced by people outside of individual purchase decisions as a result of those decisions), or it may be artificially creating a new externality so that the decisions less-accurately reflect real net utilities, but in either case its not removing choice.