My philosophy is not to leave any permanent traces of my outings in the outdoors. The saying leave only footprints probably applies. But when you start splitting hairs about what really matters or bothers you that people do in the woods, it becomes a different story and very individual.
The saying about cigarette butts sort of applies.... someone drops a cig butt on the ground and somebody gets upset for littering, "What if a million people decide to drop their one cig butt on the ground here?" The same analogy could be applied to cutting your initials into a proper tree (not old growth timber which does not exist in many places), graffitti in general, building shelters, a campfire, cutting and using downed dead timber for a fire, clearing a camp site of debris or cutting small trees to use around the fire or to support a tarp, driving on wet dirt roads, ATVs, mountain bike use off road, or whatever. The list is endless and it is all a matter of perspective on the outdoors and man's impact on these areas. Man alters his environment no matter where man goes to some degree for his own betterment. That is what makes man different from most animals. So, yes, some judgement is necessary when altering your environment. That is where the problem lies, a 40 or 50 year old man who has spent many hours hiking and enjoying the outdoors sees things differently than many adolescent kids or a hard core Greens Peace or Sierra Club person in terms of the importance or relevance of man's impact.