IMO forcing law abiding citizens to associate with criminals is inflicting damage on them without a necessary justification.
A fenced-off city that will inevitably be compared to a Holocaust ghetto.
But why's that a bad thing?
Yeah a massive walled city would be cheap to patrol and run. Put it where Pelican Bay is.
"There'd need to be laws to prevent discrimination against people with collars, though."
Why?
I was imagining a world where creationism was true.
According to this, there were only 9 billion humans alive before the agricultural revolution, as compared to 109 billion who have lived and died:
"But when you're on the receiving end of such "statistical" ostracism from everyone you meet, it feels quite different."
Do the feelings of the shop owners count?
In fact we already know how this works today, as many employers do not hire criminals and many landlords will not rent to them. Others do, money is money. The system works, criminals don't face ostracism from everyone, they have one another and many non-criminals who are willing to associate with them. (Many criminals are even willing to almost implement your suggestion with face tats.) It provides deterrence of crime and, more importantly, preserves the liberty of the non-criminal population.