In Sri Lanka and India the rule is eat with your right hand, and wipe your ass with your left. This is a widely spread system and one that on the surface seems to make some sense: leave one hand for the dirty work while sparing the other for all that should be done hygienically.
However when you wash your hands well, you have to rub both hands together. If you don’t believe me, go take a dump now, then wipe your ass with your hand and then see how much of the crap you can effectively get off it while only washing that hand with the fingers of said hand. And if you are wiping your ass with your hand, you’d better be cleaning it well, so you better be washing that hand with both hands. But now if you do wash it well, using both hands, in doing so you’ve now combined the previously divided and designated hands, using the shitty hand to clean the foody hand, and the foody hand to wash the shitty hand, until they have both reached some foody-shit equilibrium with one another. The divide is gone and my argument is thus that it doesn’t matter which hands you do what with, since upon cleaning, this sacred rule of task designation will always be made completely redundant.
A Sri Lankan may then argue that it is not the actual physical logistics of the rule that are important, but merely the psychology behind the rule. They may say that there is something to be said of the peace in knowing that you are not eating or shaking hands with a hand that has previously been flickering through ass hairs for rogue pieces of poo, that it is a case of mental depiction over actual effect, just like how someone may still not want to eat something that has fallen on the floor even when provided with proof that the food did not pick up any harmful pathogens.
However to this I would say… how about you just don’t wipe your ass with your hand?