An Excise Tax is Not a User Fee
Governments apply excise taxes to private market transactions. User fees, on the other hand, are costs associated with a publicly owned good. While some user fees are calculated in accordance with the perceived cost of a good or impact (bringing an RV into Yosemite costs more than driving in a scooter), these fees are unlike ad valorem taxes because they involve access to state-owned assets or services. When a citizen pays a user fee to obtain a drivers license, he is essentially re-paying for access to roads that have been built with his money.