Your argument that you yourself won’t catch something if you don’t wash your hands after a shite has a “ring “ of truth to it . The pathogens in your own alimentary tract by the very reason that they’re inside your body won’t , but not on every occasion , cause you any harm , unless ingested or injected into an area in greater numbers than is the norm , or when your immune system is down .
But your bacterial flora is inherently different from anyone else’s . The problem with not washing your hands and other people doing likewise is the the very real possibility that their bacteria gets into your system and in very minute quantities ( there is about 100000 bacteria on the head of a pin ) can cause a pathogenic reaction . You can lick your own shitey hands clean if you like , just don’t touch areas in the surroundings that other people may come in contact with . That’s just basic human decency