> I'm concerned by the fact that he allows himself to go to such a place without applying the precept "Leave no trace".

You can't "leave no trace". The animals that noticed you behave differently now. Your footprints diverted an insect. (And, if you were riding a horse, the water that pooled in the hoof prints kept a Texas Ranger alive.) Your "waste" poisoned one thing and provided nutrients to another.

You can argue that these things don't count, but the line isn't as bright as your aesthetic revulsion requires.