Why is it thin? There are several studies showing how policing reduces crime through a couple of measures. Intuitively it would make sense that locking up cri

Why is it thin? There are several studies showing how policing reduces crime through a couple of measures. Intuitively it would make sense that locking up criminals would reduce crime (making them unable to commit more crime), that increasing the chance of a criminal getting locked up would reduce crime (via incentives), and just seeing more police officers around would reduce crime. I would be really surprised if for the past 1000 years, civilization was tricked into believing in a criminal justice system was necessary when in reality it wasn't. Are there any studies where they dramatically reduced police presence and crime wasn't affected?