Humans in the past, like humans in the present, have the ability to see, smell and taste their food. We are highly sensitive to the signs of purification of meat.

I'm sure that most of our ancestors had a higher parasitic infection rate - but that doesn't necessarily cause chronic illness like what we have today.

Dogs and pigs literally eat poop - their own and others. And they live. Cats lick their butts. We are not so fragile in that sense.