Can you explain the hate for rock cairns to me? I don't hike so I'm not creating them, but to me they seem to violate the letter of "leave no trace", but not the spirit.
Littering saves yourself the hassle of cleaning up after yourself. Leaving crash pads behind serves a need for safety. These are selfish acts that benefit you for practical reasons while ignoring the well-being of the environment around you.
Rock cairns, while (probably) less damaging, serve no purpose other than leaving a trace for the sake of leaving a trace.
The problem with emotional acts is that it provokes different responses in people. An innocent stack of rocks gets bested by a bigger one. The bigger stack gets bested by a wider one. The wider one gets trumped by a painted one, and so on.
Look at the example of Mt Everest. Many parts of it are a high altitude garbage dump, turning a unique place into a sort of monument to the throngs of bored dentists looking for a thrill.
Definitely interesting to explore these boundaries.
The people who are against music and cairns in parks are not protecting any natural law. They are protecting their specific terraforming project, a park. It is driven by a purely human concept of "sustainability" and cannot possibly be something that existed in a world without humans.
Now, that is a nice terraforming project they are protecting (notice how "nice" is another human concept?) We also tend to spend a lot of energy protecting species that trigger the same neural pathways in our brains as human babies, even if the species would most likely go extinct without our intervention (pandas).
What environmentalism actually does is act as a brake on our other terraforming projects, allowing us to go on terraforming longer and not turn our environment into something inhospitable. But even that is entirely anthropocentric.