They have no right to disallow photos. Salvation Mountain wasn't built by them and has become an artwork that belongs to all.
I came in with a an attitude of seeing something interesting, as featured in several internet documentaries. I had no communication with anyone. I stopped, opened the door of my car, stood up, and took a picture: https://imgur.com/NyzDKgJ
Then they came out walking quickly towards me in a threatening manner. I had hoped to actually walk around the artwork, but they had posted no photo and keep out signs. My attitude didn't sour until after I felt threatened and feared that I would get shot.
Was it entitlement? It sounds like entitlement.
The inappropriate entitlement is from whomever put up those signs and harasses people when they come near.
Ok. So be it.