this is an old issue, and not a simple one, with a one size fits all solution.
if there's an existing clear trail, adding cairns is visual trash.
if there's an existing faint trail, where those who are not Danial Boone may wander astray, then maybe an occasional cairn is warranted.
if there is no trail, but its a well used area, then maybe cairns are justified in order to create a use trail and minimize damage to the environment.
if there is no trail in a seldom used wilderness setting, the question is more iffy in my mind.
do you use cairns to keep people from getting off course, or do you not have cairns in order to preserve each persons wilderness exploration experience?
here, I think it depends on the terrain, and you need to take it one spot at a time, no blanket rule.