It is indeed insidious in that the general public has no way to know the place is private and not public space.
(Source: Working in Canary Wharf on and off for 8 years)
Owners of privately-owned public spaces (POPS) need not delineate their property boundaries, or provide any kind of indication when someone may be crossing from a truly public space into a POPS. Owners of POPS may establish rules of acceptable conduct for their space, but are not required to publish them. The only way to discover what those rules are is by breaking one, at which time they may be enforced without prior warning, and with no due process or appeal. The rules may be changed at any time, for any reason, with no notice.
That system is so arbitrary and capricious, and so broken, that I can only conclude that it is entirely incompatible with liberal democracy. It is the very soul of plutocratic, pseudo-libertarian oligarchy.
How do you feel when you enter public (government) property, but they make available for you thousands of pages of by-laws that govern your behaviour? Is it oppressive?
Malls have no entry fee, but they often post their rules on their websites. I don't feel very oppressed by them, because I don't frequent malls much. I didn't even visit often back when they were popular. Places like Universal City Walk or Disney Springs in Orlando are actually like Hell for me, crowded, noisy, and commercial, and I am pretty uncomfortable with how the Reedy Creek Improvement District is like an independent fiefdom, and the acme of all tourist traps. It sometimes feels like you could be black-bagged and whisked away just for showing too much stress on your face and not having enough money in your pockets.
Yes, that's oppressive. And creepy. I don't like it when people look at me like I'm either an overflowing bag of cash to be drained or an unpleasant insect to be shooed away.
Rules for public land use are frequently organized by intent, and one does not need to read every last rule on every last page to enjoy any particular use. If you are just day-hiking, you don't need to read the parts about hunting or overnight camping. If you also want to camp or hunt, you can read those sections and not also the parts about cell tower sites or water rights. You also have the knowledge that if any rule for use of public land conflicts with your rights, it is void from the start, and if someone attempts to enforce it against you, you will likely eventually get some compensation.
But I have also read some of those thousands of pages of rules, and in some municipalities, yes, they are oppressive. In others, they are mostly reasonable. That also depends in part on the strictness and uniformity of enforcement. Policing for profit can make reasonable rules oppressive, and oppressive rules, laxly enforced, don't seem quite so bad when there is no real penalty for breaking them. In either case, the locals usually have some means by which to change the rules that they may disagree with, including loud and well-attended protest demonstrations.
The danger of POPS is that they replace some of the functions of truly public spaces, while leaving out one or more vital functions (like protest and free expression), then those public spaces wither and die, leaving people effectively unable to exercise the vital functions.
Given that e.g. large parts of the pedestrian routes along the Thames for example are private, there substantial stretches where you can't even stand and take pictures of the river where no part of said private property features in the picture, because the property owners have instructed their security to just blanket refuse all permission to take pictures.