Yes, plant and animal matter are both organic and both decay. Plants just decay a little slower because they have hard cell walls. Also, you're so disgusted by plants being fertilized with human feces? Do you know how the food chain works? Did you take 7th grade biology? Why do you think plants grow? Because nutrients in the soil are replenished by dead animals and FECES! It's not that important what animal the feces comes from, as long as it contains nutients like potassium and nitrogen. Human feces are traditionally not used for fertilizing because they can contain human diseases, but if properly screened and processed, there's no reason they can't be used.

Also, I understand that a big reason for recent plant-based E. Coli outbreaks is that migrant workers out in the fields aren't given proper bathroom privileges, so they just take a dump right out in the fields and then irrigation systems transfer the feces directly to the plant surfaces. Yum!