I take a lifecycle view. Early on, public subsidy of research is necessary. US President Carter and the Germans did a good job with that for solar. When you hav

I take a lifecycle view. Early on, public subsidy of research is necessary. US President Carter and the Germans did a good job with that for solar. When you have a mature product 50 years later, that's when tax policy and/or industrial policy becomes more impactful. Industry itself is doing most of the innovating at this late stage, so you want policy to nudge existing consumers towards the preferred substitute. None of these policies are competing with one another, they are complementary. You can even use the tax revenue to fund the early-stage research of other moonshot technologies.