Websites are absolutely someone's intellectual property. Just because I've watched a Disney movie on my phone doesn't mean I'm allowed to download Disney movies from Disney+ and start my own competing service.
Websites are just some data and code that their servers send to my user agent. Once it's in my computer, it's under my control. Executing code and rendering elements are privileges and they can be revoked in case of abuse. If it's important enough to me I'll reverse engineer the website and write my own code to do what I want with zero foreign code execution.
I wasn't referencing intellectual property. Re-phrased: "It's their premises."
For example using an adblocker on my PC while viewing a website is perfectly legal. Same with scripts that interfere with tracking.
Now, if I go to the physical store and remove posters and cameras, I bet that will lead to some more resistance.