I had started a post about 1.5 years ago on this very topic:
https://mooneyspace.com/topic/45873-big-brother-landing-fees/
At that time, I wrote to AOPA and this was the response I got. I had posted this response under the original thread, too.
Thanks for your email. Yes, that is completely legal. Airports are free to charge landing fees and can use human observation, cameras, or other means to record them. Vector Airport Systems is at many airports. If you have been charged in error that definitely would not be acceptable and you should reach out to Vector Systems to correct it.
At this point, I'd pick my battles. I (personally) am perfectly fine paying the 20-30bucks at places like Gatlinburg, Titusville, Centennial where I actually got great service. So maybe my beef is with in-the-middle-of-nowhere fields or "mandatory shacks you must pass to exit" where they want to milk people.
I think we should also acknowledge the world we live in.
#1 general aviation is seen as rich boys' playground. One recent example is this post https://www.facebook.com/photo/?fbid=10222217339017137&set=gm.8789214651174518&idorvanity=443036732459060 Look for Mr. Peter Barry who wrote this: "What a bunch of Rich whiners!. You tiny minority of Rich aviation people who want to fly in because it's cool. Has nothing to do with wilderness and its values. Your private, selfish wealthy act of flying in and around the wilderness ruins it for thousands of other people will actually value wilderness.. The solitude the beauty, the quiet the long long hike to get in.... Go whine somewhere else." So in the eyes of jealous losers, killing GA will be an act of "social justice." They'll attack with leaded fuel, then with noise, then with affordable housing on airport lands. They'll never stop.
#2 As cities and towns expand, airports get engulfed. We are on the same boat as race tracks, shooting ranges and (lo and behold) farms for that matter. Yes farms. People buy houses next to farms and then complain about the smell. But this expansion of towns drives up property taxes, too. I heard from some airport managers that FAA grants are used for upkeep and renovations. If the hangar fees, fuel profits, etc. do not cover the expenses, the very capitalism would require the closure of the airport unless it's useful for some other purpose. "Playground for rich whiners" does not qualify...
#3 Airport accounting. Though airports are allowed to charge landings fees, are they doing it to beef up their profits, or is it because they want to square their books with the rising costs? Are they being managed properly, or is there a lot of waste that could be prevented? I guess there, being an active member of the airport admin would clear any doubts.
Other than that... Frankly, if landing fees are justified, I'd rather pay an automated system than a human - because a human collector would require much higher fees to cover their salaries, and not to mention a reduction in airport opening hours. Have you ever been denied landing in perfect day VFR because the airport was closed 6min ago? It hurts.