To a very large extent the airlines and passengers are the ones who pay for these things. Passengers get dinged for PFC charges, fees and taxes. Airlines pay fees to the airports, among other things.
As just one example, ATC is primarily funded through excise taxes that are imposed on passengers.
In 2018, Southwest paid $1,334,000,000 in landing and airport fees - which equates to $8.15 per passenger. Source:
https://www.sec.gov/Archives/edgar/data/92380/000009238019000022/luv-12312018x10k.htm
By comparison, Amtrak paid $59,400,000 in freight access fees in 2015 - or $1.92 per passenger. (Yes, I know this is complicated by the fact that they own the NEC track.) Source:
https://www.amtrak.com/content/dam/...nualReport/Annual Report Fiscal Year 2015.pdf
People who complain about the funding of air travel need to be careful for what they ask for. If you truly want to start leveling the playing field from a passenger perspective, the taxes on an Amtrak ticket need to go up.
That said, I don't see it as a zero-sum game. I believe that air
and rail transportation should be supported by the government. They both serve an important role.