Among the dogmas of the left is that putting people in prison fails to reduce crime and that the social "root causes" of crime must be dealt with to prevent it beforehand and that "rehabilitation" through various programs "in the community" are more effective than locking up criminals.
None of this is new and the rationales for it go back at least two centuries. What is remarkable is how mountains of hard evidence to the contrary have been ignored, evaded, or simply lied about, on both sides of the Atlantic.
David Fraser's book "A Land Fit for Criminals" examines that evidence at length and exposes the fraudulence of the claims used to try to justify continuing to be lenient to criminals as crime rates have soared in Britain.
There are similar mountains of evidence against the left's crime dogmas in the United States and this evidence is similarly ignored, evaded or lied about by those on the left. It is just that the left faces stronger opposition here so that it has not achieved the pervasive dominance that it has in Britain -- yet.
In both countries, ideologues have the support of "practical" politicians and bureaucrats who simply do not want to spend the money needed to build and maintain enough prisons to put career criminals away for many years.
Those weighing costs and benefits define "costs" as government expenditures. But the costs paid by the public, just in economic terms, vastly exceed the cost of more prisons. But that does not count for either the ideologues or the "practical" politicians and criminal justice bureaucrats.