There used to be special drugs for those who worked in the city's biodesign labs. There is only so much that can be done to living beings before even the most horror-hungry minds break at the sight of things too strange and too familiar. The drugs shut down the parts of the brain that would go insane at the awareness of sentience where there shouldn't be any and the encounter with degrees of humanity obscenely fine. Without the drugs no progress was possible beyond a certain line farther but stronger than mere decency or disgust.
With the drugs there was no line. So the people who controlled the city — in places so high they did not need the drugs — decreed that the things and no-things created in the labs were too useful to be kept there.
Now there are special drugs for those who live in the city and for those who visit. There are very few images of its streets, none of them unedited. Almost nobody who enters the city ever leaves it. Those who do still have to take the drugs forever, for the simple memory of some things is enough to turn to madness anybody biochemically capable of going mad.
(But nobody begrudges the deal. The city is rich. The city is powerful. And in places even higher than those that merely control cities the city that was an expedience had become a prototype.)