Coccidia are in the soil- everywhere. All chickens build up a resistance to it. Younger chickens sometimes get overloaded with it and it damages their intestines. Hence the need to treat so the chicken can heal, so it can get resistance.
Oh please don't cull for coccidiosis! It is so easily treatable with medication (but fast and deadly). Once they get their resistance then you are out of the woods.
As far as eating the eggs, I wouldn't eat them if you are giving medications unless there is no egg withdrawal period. If they aren't on meds, then I can say that you have to decide. I would eat them if it were me, but I'm not going to tell anyone to eat eggs.