In reply to Webster:
I don't think you're completely wrong there, but I don't think it's really that simple.
Human faeces is effectively 'dirtier' for humans than that from most other animals, as it can spread human diseases. I'm led to believe it generally smells worse to humans, too. (It's not that I'm not human, I just can't smell stuff!)
I've done a fair few al-fresco poos over the years. If it's a distance away from places people spend time (the foot of a climb, a hill summit, or the like), it's not by running water, it's somewhere it can degrade quickly, and it isn't visible from a distance, I don't see a problem with it.
But in a cave, where people might shelter and where it will never rain on it? Not good!