That's pretty unfair, the parent explicitly differentiated between navigational and aesthetic purposes. The former is a critical part of any trail more remote than a boardwalk, while the latter for someone's FOMO insta post.
Maybe someone's insta post is their critical part of their experience? Maybe they want to build cairns because they think they are beautiful. Who cares, it doesn't affect to environment as badly as a well traveled hiking trail with clear signage that attract lots of tourist who leave trash.