Can he [the landowner] ban anything at all and if so what circumstances justify doing so?
Izzy answers, making up his own 'law':
He can, but only with advance notice.
For example, he might invite you onto his land on the condition that you sign a waiver, acknowledging that the landowner will shoot you if he feels like it.
You'd be a fool to sign the contract, but if you signed it and entered his land, he'd then be within his rights to shoot you.
If, on the other hand, he invites you to dinner and up and kills you, he's a murderer: his invitation implied a contract not to harm you during your visit.
That isn't a limitation on his property rights; it's a case of a voluntary contract waiving certain rights.
He can make absolutely any rules he wants, but he can't then change the rules at a whim. This answers your original objection, but leaves open the possibility that he might lawfully organize a "paintball" game using live ammo.
The law doesn't work that way today, however.
Courts do not respect the liberty of contract, so for example a contract to provide assisted suicide, or sexual services, would be nullified by the courts. But I think it was already clear to you that we're discussing "shoulds", not current US law.
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Kris, what we have here is 'bold' evidence of a very naive mind. -- Izzy and I started out discussing the 'implied social contract' aspects of the US Constitution. [a very libertarian document, to my mind]
Now izzy wants to claim that all along he has been arguing utopian libertarian theory. --- [IE -- "you {can} ]sign a waiver, acknowledging that the landowner will shoot you if he feels like it."]
Bizarre stuff.
Rational libertarians agree that our US Constitution is a valid social contract based on the free will of everyone who resides in this country. Any individual is free to renounce citizenship and/or leave to avoid honoring our Constitution & its valid laws.
But it is implicit, -- that if you stay here, you play by Constitutional rules. -- [you do not ban guns in your parking lot]
It's the most libertarian document ever produced. That doesn't mean it's perfect, of course--but if we have to have a government at all, I'd take the one Jefferson envisioned. But don't act so surprised that my scope is broader than America as it is! The founders tolerated slavery, yet I call it "wrong," so it's clear from the get-go that I have points of disagreement with the founders' original intent.
Rational libertarians agree that our US Constitution is a valid social contract...
Libertarians deny the existence of "social contracts". You're engaging in special pleading: instead of arguing for social contracts' validity, you're asserting that anyone who questions it is an idiot.
"Kris, what we have here is 'bold' evidence of a very naive mind."
I observe that your style can be more direct than mine. (That's an observation not a criticism.) You sometimes (not always) post what I might think.
Primarily as an exercise in self control I try not to post such thoughts even though I sometimes fall to the temptaion--and brother, I am certainly tempted sometimes.
In any case, I absolutely see where you are coming from.