Fascinating article that covers the history of organic, virtues of poo and mineral/chemical fertilizers. I'm still reading through it but so far I've found it to be very reasonable from a scientific point of view. And it's an easy read, too.
http://www.soilandhealth.org/01aglibrary/010178.better.than.organic.pdf
http://www.soilandhealth.org/01aglibrary/010178.better.than.organic.pdf