The user fees have NOTHING to do with ICAO compliance like age 65. You should know better than to put up a swiss cheese argument like that.
All it is, is a money grab. The ATA fought off the EWR slot auction, just like EAA and AOPA are trying to fight off user fees. You know that the problem that the airlines are crying about is their own doing. If the airlines cut 10% of the number of departures, but used larger airplanes to cover the capacity, there would be no uproar of "GA plugging up the NAS". If an airline is VOLUNTEERING to give up 3 slots per hour to fix the problem at LGA, why the heck is the DOT/FAA willing to go with the plan? Once they take and never use AMR's LGA slots, and don't allow the gross over-scheduling of EWR, all of a sudden the airlines will be operating someone efficiently, and they won't be crying wolf at an excuse that doesn't exist. All the user fees are from the ATA's standpoint is a scapegoat to cover their own incompetence.
As for GA mixing it in with the airlines, any proficient pilot can do so quite easily. SNA has 2 runways, one is used exclusively by GA. While I've never flown into SNA, I have taken a 172 into BOS. Its the same deal there. You have to know what is going on, ATC will keep you out of the way, and it will all work out. All the problems that you have mentioned about SNA are not a problem with the NAS, its with stupid pilots. User fees won't fix stupid.