I read this whole thread, genuinely intrigued. It seems there are certain things it is acceptable to trespass and do, and some that aren't. And that the size of your own private property determines which of those things are OK.
It would seem that if you have a field and a long drive, you should accept people who have planned their journey poorly to pull up and sleep there, possibly using your land as a toilet. But having a picnic is below the belt. Unless you have so much land that you can't see them doing it, so that's alright. If you only have a small drive or a patio both camping and picnicking are a poor show. 
I'm spotting inverse snobbery dribbling out all over!
Would anyone care to hazard a 'right on' way of dealing with the problem I had not too long ago? I have land (get me!) and it borders a large forest which is heavily populated with all kinds of edible wild birds. I was alarmed to notice a chap wandering round with a large gun one day. I didn't give him a cup of tea and a bacon sandwich, I didn't give him a couple of hours to see if he would go of his own accord. I rang the police. It turns out it was a neighbour's adult son, who was shooting pheasants for his tea and thought I was overreacting by ringing the police. Besides, he reckoned I shouldn't mind him shooting pheasants on my land as the pheasants are not mine and he has no land to wander with his gun on.
I've also been threatened with legal action by a trespasser because he was climbing up a ladder in my field (don't ask - the neighbour again! He's a bit odd,) and my horse, which lives in the field, scratched his bottom on the ladder knocking it over. Which apparently makes him a dangerous animal. 
It does seem as though some people who don't own any more land than their own garden think that any larger parcel of land should be available for everyone to use.
As for the 'class warmongering' comment - you silly person. Stop warmongering and get out and earn enough money to buy your own bit of land if you are jealous. It's what I did (and I started from very humble beginnings.)