—to undo its revenue neutrality.
I don't know whether there is a best answer to that. Ultimately, these are political choices.
I also didn't say that the best carbon tax is one that is revenue-neutral, although I think there are great benefits that come from revenue neutrality. It is certainly the case that a carbon price can be very effective, even without increasing the scale of government at all.
Carbon pricing is not about increasing the scale of government. It is about changing prices and changing behaviour. You can certainly return every penny of the revenue to the economy in some form, and you can certainly do it by reducing income taxes or other taxes, and you will get economic benefits from doing so. There are, however, many choices. This is another political choice: whether you want to use the revenue to replace crumbling infrastructure, as in Montreal, where I come from, or whether you use that revenue to reduce income taxes or to pay back debt. There are many choices.