If you can't go out into nature without trashing it, just stay home.

When I got hike, I just started taking a trashbag. Was on a waterfall trail in Colorado three weeks ago; someone left a sock, another their _entire pants_ in a tree (we checked around before cleaning them up, and it was obvious they had been there awhile). How you forget your pants is beyond me.

And don't get me started on people's stupid dogs. Dog feces is pollution, and is non-natural in these environments. People will sometimes scoop, but then leave the bag. What part of that is acceptable?