The point is to discourage carbon-profligate behavior by making that behavior more expensive. If you increased cigarette taxes and used it to lower other sales taxes that would still reduce cigarette use[1]. Maybe you'd get even faster reductions in smoking if the cigarette taxes were all earmarked for R&D on ways to end addiction, but making something more expensive tends to reduce consumption of it regardless of how the tax is later spent.
If you're wondering "why not use targeted legislative mandates instead of carbon taxes?", I'd say that taxes have an advantage in that they're harder to game and need fewer adjustments over time. For example, if you introduce a mandate to make cars more fuel efficient, manufacturers will tweak the vehicles they sell so they are no longer "cars" but some legislatively distinct class of vehicle, and people who like gas guzzlers will just drive those tweaked vehicles. But if instead there's just a carbon tax on fuel it's a lot harder to game your way around the legislative intent.
[1] Assuming that the balance between just paying the tax and evading the tax still favors paying it. You don't want to impose a $20/pack tax and find that you've just given organized crime a major boost.
If you're wondering "why not use targeted legislative mandates instead of carbon taxes?", I'd say that taxes have an advantage in that they're harder to game and need fewer adjustments over time. For example, if you introduce a mandate to make cars more fuel efficient, manufacturers will tweak the vehicles they sell so they are no longer "cars" but some legislatively distinct class of vehicle, and people who like gas guzzlers will just drive those tweaked vehicles. But if instead there's just a carbon tax on fuel it's a lot harder to game your way around the legislative intent.
[1] Assuming that the balance between just paying the tax and evading the tax still favors paying it. You don't want to impose a $20/pack tax and find that you've just given organized crime a major boost.