This is the only correct answer. Humans do "prolapse" our anuses when straining to poop (it's how/why some people develop hemorrhoids and why you are told not to a strain if you are prone to them). Plenty of animals have poor diets that lead to occasional diarrhea and constipation, especially wild animals in scarcity conditions or strays in urban environments. (Household pets at the mercy of their owners, too.) And anybody who has been camping knows that squatting may be more comfortable and let you poop easier, but it doesn't negate the need to wipe.
All mammals have buttholes. Humans are among the rare mammals who have butts, too. And our butts don't allow for, um, exposure and ventilation.
If you stick a wad of gum on a napkin and leave it that way while you are eating, you'll be able to pick it off cleanly. If you squash the gum between two halves of a folded napkin, it'll be spread around and get stuck and it will be much harder to clean. Same principle, except add bacteria and waste to the equation.