There was a programme on TV here a couple of years ago about this. From my vague memory of it, the human waste ferments or something, which generates enough heat to sterilise it.
Though the concept seemed a bit iffy to me.
It’s about as safe as any other manure used as fertilizer.
Because it is dumped on the ground, rain & groundwater & microbes start ‘composting’ it into the ground, it is absorbed by the roots of plants, powers growth of the plant, and production of crops. It has gone through quite a bit of conversion before becoming an edible crop, and is no longer at all dangerous.
The danger comes when this fertilizer is splashed onto the growing crop, and is not washed off by rain or by washing the picked crop, and it is eaten raw. So that people are actually eating crops with untreated human sewage splashed onto them. People in Asian countries have learned not to do that – they wash their picked crops carefully, often peel them, and generally cook them before eating them.
Psychological reasons. What we perceive as a ‘good’ or ‘bad’ smell is taught to us when children as part of our culture. (And varies between cultures – some cultures like smells that other human cultures dislike.)
But in nearly all human cultures, the smell of human waste is considered one of the ‘worst’ smells. [Presumably, this served an evolutionary survival purpose – humans that disliked this smell and thus avoided it, and buried or burned human wastes had less exposure to certain diseases, and thus a slightly higher chance of surviving and reproducing.] So human manure would be considered to smell worse than other manure.
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but swerving back to thread question, it’s not impossible to handle human feces in a safe and hygenic manner. no japanese has ever been accused of being filthy (i could be wrong on that.)
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Scroll through enough Web porn, and eventually you’ll see that the Japanese, in fact, are past masters on that point.
^
you got me there.
Just spread some human feces on my yard. 
Golf course greensman use Milorganite. It’s Milwaukee treated sewage. Fully treated and sterilized to kill any pathogens. My local Farmers Coop sells it by the single bag. I’ve used it for years on my lawn and flowerbeds. Very potent stuff and it doesn’t burn plants. It has a strong uric acid smell but no poop smell. I’m surprised more major cities aren’t producing this stuff and selling it.
Years ago, my uncle had chicken houses. We put down sawdust shavings before getting our laying hens (10,000) and roosters (1,000). All his eggs went to the hatchery. At the end of the 10 months laying period we removed the shavings/manure and used a spreader behind a tractor to spread it out on his pasture. He’d also give family bags of it to get grass growing. Stunk like hell, but it was the most potent fertilizer I’ve ever used in my life. That stuff was like liquid gold. You just didn’t want to walk on it for a few months because there were still juicy turds to stick to your shoes.