America abandoned a custodial approach to mental illness a half-century ago, and the results have been obvious in the nation’s streets and public spaces ever since — and never more so than on the Bowery early Saturday morning.

Now Albany is moving toward the same non-coercive approach to crime and criminal justice — they call it “bail reform,” among other things — and the impact on New York’s already chaotic streets is certain to be dramatic. Just think of it as the latest insane embrace of social disorder and stand by for stormy weather.

The Bowery has been a last stop for the down and out since forever — well-known for moral dysfunction and urban despair, though not so ­often for bloody murder.

Enter Rodriguez “Randy” Santos, by most accounts a toxic broth of insanities, addictions and violent impulses so profound his own mother is said to be terrified of him. Police allege he savaged five fellow Bowery derelicts with a makeshift iron wrecking bar in the twilight hours, killing four outright and hospitalizing the fifth with critical injuries.

Santos is in custody, and thus now begins a complex adjudication process focused almost solely on him: his actions, his incapacities and his legal culpability. His victims, and the safety of the city itself, are very much on the periphery.

Ditto the matter of whether Santos should have been on the streets in the first place. He had 14 prior ­arrests, apparently was out on bail for at least two violent attacks, was said to be a crack addict and, it seems generally agreed, was howling-at-the-moon mad.

He is a poster child, forgive the benign analogy, for a return to ­aggressively custodial approaches both to mental-health treatment and public-safety policy.

For certainly Santos wasn’t alone out there. Beggars, addicts, scammers of every stripe and the helpless, severely mentally ill have overwhelmed the city’s boulevards, parks and mass transit.

Thus it has been to one degree or another for 50 years, ever since ideologically inspired mental-health policy makers began to shut down large state insane asylums — those words used to mean something — in favor of non-coercive, so-called community-based treatment.

The new policies, made possible by advances in psychotropic-drug therapy, largely were driven by 1960s-era “liberation” activists not dissimilar to today’s so-called ­“social-justice” zealots.

They subordinated clinical needs and realities to ideology, and the new ways led directly to concentrations of blighted hotels and shelters for drugged-up, non-functional former patients; long prison terms for those who ­reacted violently to the pressures of unsupervised life; the legions of hopeless street dwellers and, inevitably, to homicidal subway pushers and associated maniacs.

And now to Rodriguez “Randy” Santos.

But some lessons are never learned, and now New York is making matters worse — mandating the release without bail of defendants charged with a variety of offenses and thereby drastically curtailing a judge’s ability to protect public safety in potentially serious criminal cases.

The new policy — which police and prosecutors across the state are calling a “catch and release” program — begins Jan. 1. Thereafter, judges will be required immediately to free those charged with criminally negligent homicide, aggravated vehicular homicide, manslaughter in the second degree and assault on a person less than 11 years old, among many, many other serious offenses.

It’s hard to understand how eliminating judicial discretion in such cases will make for a safer society. And of course it won’t, because — just as with mental-health policy 50 years ago — safe cities simply don’t matter to the activists making the decisions.

If they did, it’s equally hard to imagine Rodriguez Santos being on the streets in the first place.

But while social justice truly matters, that cuts two ways.

Saturday’s victims will pass from public notice soon enough; life having dealt them losing hands long ago. But they deserved better than dying at the hands of a ravening lunatic because society long ago lost the will to restrain such people.

Just as New York deserves better than what’s coming — also because its leaders simply can’t say no. And where’s the justice in that?

Twitter: @RLMac2