> Ah okay, laying a few stones is ecologically sensitive, but if a billion dollar company wants to dig up the entire beach for a cable, that's not a problem.

The billion dollar company is monitored by ecologists and other professionals to make sure they build things according to environmental impact laws and follow their permits (e.g., after digging, restoring the top soil, etc).

Randos moving and stacking stones, especially in large numbers, may alter habits for (small) animals and cause erosion:

* https://www.ausableriver.org/blog/leaving-no-trace-rock-stac...

* https://science.howstuffworks.com/environmental/conservation...

* https://www.nps.gov/articles/rockcairns.htm