User fees require an entirely new bureaucracy to collect the money (which,
of course, is the REAL reason the government-types want them). If more
money is needed to pay for the FAA (a concept which is ridiculous in itself,
but I digress), higher fuel taxes can and will pay for the shortfall
efficiently and quickly.

Oregon tried that 20 years ago to fund their state aviation programs.
People stopped flying as often so the revenue stream declined.
The programs still had to be funded so the state went back to the old
way of doing things.