If you fly in uninvited, I agree 100%. It's no different to picking a field at random and hoping it's OK. The owner should have no liability.
But if a strip is open to visitors, either open or with PPR, then the owner should not leave it in a dangerous condition. Potholes cannot be seen from the air. Some cannot even be seen from the ground; the only way is to walk the route before taxiing.
I think the "burglar injuring himself" is a redherring here, and is indeed an appalling travesty of justice in the cases where he was able to sue. A trespasser should be able to kill himself and it should be fair game. I think the reason why such people have been able to sue is because to have it otherwise would enable homeowners to set lethal traps for intruders, and that is illegal, and arguably (very arguably, I admit) wrong. But it is still wrong in principle, as I am sure most people would agree.