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.../When you ask them to prove it, they most likely will feel threatened and jump ugly. Then they will issue a ticket for creating a public nuisance..../
I started out in law enforcement in the mid 1980s and got out after a couple years. Even then attitudes were changning from "to serve and protect" to "us against the civilians" and "whatever it takes to get home tonight". At the time about 5% of the officers generated about 90% of the complaints about over enforcement, but it was clear that percentage of officers was going to rise.
In part I blame much of that on moving from a uniform with dress pants with a stripe on the side, a tie, those horribly hot heavy polyester dress shirts, and concealable body armor under the shirt, to a uniform consisting of tactical BDUs with tactical body armor on the outside. When officers started dressing like military personnel they started acting like it. It made an insecure officer's inclination to take charge and control the scene, without determining what was actually going on, far more likely, and it decreased the likelihood that an officer would appropriately use discretion to maintain order, rather than rigidly enforce the law. It also empowered officers with ego issues to feel even more that "contempt of cop" was an actual offense.
Much of it was blowback from Reagan amping up the war on drugs, spouting hyperbole about the threats posed to officers, and increasing the flow of surplus military equipment to police departments. Reagan was very pro law enforcement, but there were unintended consequences that we're still struggling with today, although I think progress is now being made.
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In any event yes, if you suggest to a modern day police officer that landing on a suitable piece of land with the landowners consent is legal and ask him to show you a statute that says differently, the odds are good he'll feel compelled to cite you for something convenient like disturbing the peace, creating a public nuisance, or if he's a real jerk going big with something like reckless endangerment.
If you don't want to end up in court contesting a citation, you are probably better off, looking surprise, being apologetic and advising you won't do it again.
On the other hand, you can get cited, take it to court and let the judge determine there's no legal basis for the citation - and verify that there is nothing illegal in landing where you did. That precedent could be useful.