Jordan, this is really a bullshit argument and I am sure you know better than that. I am really curious why do you insist on peddling this crap here?
Tax on gasoline is anything but "arbitrary" - it is simply an effcient means of collecting user fees for driving - which includes road construction and maintenance, removal of debris and pollution, traffic law enforcement and policing, etc. Those things cost money, a lot of money, but ther drivers are not paying for using these resources - the taxpayers do. A flat tax per vehicle would be inefficient because it woul dnot be ties to actual usage, using toll booth would have a high transaction cost. Using GPS positioning devices may be a bit more cost effective, but would create many problems for civil libertarians. Therefore, taxing gasoline is the most effective means of charging user fees for driving.
The current system is is really a form of state "socialism" for cars - government builds roads and makes them available free of charge to everyone with a vehicle. If gas or electricty or any commodity were distributed that way - that would create havoc and enormous waste. If I do not drive - I still pay for the roads in the form of taxes. Since the lower income people are less likely to own a vehicle - at least in the East coast - that is already regressive, because it subsidizes the driving privilege of the more affluent who have several vehicles.
Another issue - tax policies may have different goals. Some of that involve redistribution of wealth, other may aim at changing behavior, increasing effciency or simply charging fair user fees. I am sure you can make that distinction - so why do you come with the regressive tax bullshit? Sounds like talking point scooked up by car and oil industry lobbyist. The cost of owning a car (insurance, repairs, etc) is a much worse form of regressive taxation than gas tax that subsidizes public transit. In fact, the latter would be a progressive tax if you consider all transportation costs and usages.
In Baltimore, it is mostly the poor who use transit as about 40% of city's population do not even own cars due to high insurance and maintenance costs. Higher gas cost would have zero effect on them, and would affect mainly suburban fatheads who drive SUVs because they are afraid of riding buses full of dark skin people. If anytyhing it may genrate some extra revenues to improve transit used mainly by the poor. I do not see why a progressive should have a problem with that
Wojtek