The reason you wash your hands is so that you don't spread pathogens to yourself and others. As far as I can tell, that's not the primary reason you wipe your behind.
And now semantic satiation has kicked in for "behind."
No. OP is not arguing that. OP is arguing that if you got mud on your hand and tried to clean it with dry paper, there will still be crusted mud on your hand. Do you see where this is going now?