If we're trying to assess the theory that AGW policies are strongly perturbed by politicians' alleged desire to increase taxes and regulation, then we need to compare actual AGW policies with a baseline estimate that ignores the effects of that desire.

Yes, but the baseline itself is relative to the current situation. Politicians want to regulate more than the regulation we actually have, so if you also want to increase regulation to more than we have, that benefits politicians. It may be true that you want an end point far beyond what the politician wants, but that's going to be irrelevant unless your push has some reasonable chance of going that far, which it probably doesn't.