Soylent Green is Poo-Poo! Can't you just hear Charlton Heston bellowing out this warning? And why shouldn't Soylent Green be poo-poo? Poop has plenty of nutritional value in it, it's not like our digestive systems are so efficient that they get all the food value out of poop. I think it's very likely that in the over-populated future we are hurtling towards that Mankind might turn to poo-poo for it's nutrition.
Plenty of animals eat their poop, rabbits and dogs come to mind, so if it's good enough for our best friend it's good enough for us too. Of course by the time we resort to cannibalism or eating poo-poo we would have already eaten all of the dogs, man's best ex-friends. I guess the real question here is what kind of Soylent Green would you prefer...one made of people or one made of poo-poo?