I agree that's the short-term effect (although a carbon tax will likely start out small and increase over time so as to minimize unpopular effects), but in my experience this analysis is too sophisticated for most of this "sanctimonious environmentalist" group. I.e., people who tend to believe that the environment hinges on converting people to vegan cyclists are not likely to understand economics well enough to understand a carbon tax. This is a big and unflattering generalization for expedience sake, so I'm trusting readers to understand the larger point and not get mired in "this is a generalization!" counterarguments.