Environmentally, the bag actually prevents biodegradation. If you don't pick up your dog poo in the wilderness and not where people step, some shit-eating insect (like roley-poley or cockroach or a worm) will eat it all up within a week.

Which is worse, the ones that leave a bag (perhaps unintentionally) or the ones that just don't bother with the responsibility at all? When I had a dog I not only would clean up behind him, I would leave the bag untied until the end to capture what I could of the inevitable left piles I would run across. I'm sure cart return, dog poop, fast food containers, and the old cigarette butts are all under some human psychology grouping of ego superiority.