It's a little more complicated than digging a hole in the ground. You have to ensure you don't poison the water table with run off or monsoons. Protect them from pests. Aerobic composting is simple when liquids are removed (urine separator and no black water). Pumping air through toilet chambers can help remove smells.

I live in the UK, and as I age, I seem to be loosing control of certain physical faculties. And we have a distinct lack of public toilets, which is ridiculous. You need toilets dotted everywhere which you are comfortable using.

In very highly populated areas using water as a transport has been somewhat miraculous. But it's not always appropriate. Recycling waste locally is probably a good idea where you can.

Night soil sounds primitive, but is pretty neat. Problems arise when raw sewage comes into contact with foods etc. Composting sewage, delays usage, but removes health risks and improves the resulting output.

I actually resent flushing my own turds down the toilet when my garden really could do with the input. But when two thirds of my water bill is for waste, you think twice about constructing alternatives.