Isnt the point of "sin taxes" to offset externalities? If the externalities decrease then so should the tax. If governments are looking for a steady source of income then "sin taxing" seems like the wrong approach.
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The tax on cigarettes is not pegged to the expenditures on COPD and other diseases and etc.
Afaik, all sin taxes go into the general coffers so they can't really be based on externalities. Plus the fuel tax doesn't even pay enough for road repair never mind any externalities (especially considering there's often no sales tax on fuel).