eating your own shit is still very dangerous. Yes, it was inside you, but it was in your digestive tract, and not able to enter your body from there to infect it. The reason waste is being expelled from your body in the first place is because it is un-needed or dangerous. Anything that comes out is something your body did not want inside, for whatever reason. So eating your own/ another person's shit is pretty much the same in terms of danger levels.