The nutrients in food leave our bodies as excrement. Calling that output "waste" and throwing it away breaks the cycle that should return it to the soil that grows the next meal. Organic farming that ignores the toilet is still draining fertility out of the land.
Ordinary toilets get rid of excrement by mixing it into drinking-quality water. Very little of the world's water is drinkable, so this habit spoils a scarce resource to move something that could have been kept out of it entirely.
Fear of feces, which the author calls fecophobia, is a cultural reflex that is stronger than the actual danger. The disease risk is real but can be removed by a known process, so the main obstacle to recycling excrement is the taboo, not the science. That taboo was strong enough that the book had to be self-published.
Excrement becomes safe garden soil when it is composted at high temperatures and then left for a long enough time. The health dangers come from skipping these controls, not from composting itself.
A simple toilet works by collecting excrement in a bucket and covering each deposit with sawdust, then emptying it onto an outdoor compost pile. It costs little to set up, can sit indoors, and is hard to get wrong, with no chemicals or high technology needed.