Yep and they are certainly necessary (mostly so I can walk around my garden in my onnies).
But you are making the assertion that walls always work? But work at what exactly?
- Delaying a burglar or intruder entry by 30 seconds?
- Providing a good canvas for graffiti artists?
- Not allowing my dog to escape?
What exactly are they effective at? Please be specific.
EDIT: to be clear, from my perspective walls do nothing to help me manage unauthorized entry to my property. The key elements there are cameras, beams, indoor passives, security system etc. These are the things that allow me some slim chance to actually do something about an incident.
Following your assertion all these industries and security companies are redundant? Wall should be enough?
C'mon dude look at your own life here for some logic and rationality.
Final plea: let's look at farms which are bigger properties. So farmers build actual walls around their entire properties? .... no they don't. Light fencing yes, walls no. Maybe you should ask them why not if you are unwilling to listen to us
.