There are two issues behind User Fees that I want to comment on.
Shifting the FAA budget from a tax revenue standpoint to a fee-based system takes Congress out of the loop. Now, anyone will tell you I'm no fan of the Congress, but I'm even LESS of a fan of the FAA management, and of the executive branch deciding how it's gonna spend it's fee-based revenue stream without the checks and balances of the Congress.
Second, our society as a whole (even those who never get in an airplane) benefits from the systems the FAA manages. It's proper that some of that funding come from the general tax revenues.
With that said, when someone can show me a reasonable way of determining how much cost the FAA incurs to support my flight in excess of capabilities they would already have to have in place anyway to support the airlines and military, then I'll be happy to pay those costs (preferably through an easy-to-collect system like fuel excise taxes). And I'll be understanding that when I'm IFR, I'm operating in a system sized and designed primarily for the airlines and paid for primarily by them (and their customers), and I'll understand that I may get a slightly lower level of service.
But, if you want me to pay my "fair" share of the total cost of the system. based on the number of airplanes, or to pay a fee for ATC services, than I better get equal priority, equal routings, and an equal voice at the table as any other airspace user. Which means that NWA can wait for ME instead of the other way around. And I'd better never hear UNABLE from ATC when calling for a bravo transition through ORD.