The threat-laced ramblings of alleged subway shooter Frank James, now in custody, have a disturbingly familiar ring, don’t they? Sure, they’re on YouTube — but bitter mumblings of the same sort are heard all day, every day in New York’s increasingly untenable subway system.

So the question of the moment is this: How long will the city accommodate — indeed, encourage — aggressive mental illness in its public spaces? Will it ever push back?

How many shootings, how many slashings, how many fatal shovings and — disgustingly — how many demented excrement smearings will it take before the penny drops?

How many subway cars, train and bus terminals and public parks must fill to the brim with pitiful, helpless and obviously self-destructive people before New York’s leaders have had enough?

This is not a new problem, of course — not by any means.

Once upon a time, decades ago, there was a police captain who got it. He had very little patience with a then-novel notion that therapy must always trump coercion when the violent mentally ill act out in public.

“If you knew so much about mental cases,” he’d bark at social workers, “the police wouldn’t need to be called. The reason we’re here is because you failed.”

Certainly the new policy was failing, badly. It assumed the insane were fit masters of their own destiny, regardless of circumstances and consequences — which was, well, nuts. But it had become the law.

Presently New York’s mental hospitals emptied, its public spaces grew forbidding — and decades of often lethal chaos ensued.

Kendra’s Law, a ’90s response to a fatal subway shoving, allowed judges limited authority to order involuntary confinement for the mentally ill — until then, cops and the courts were virtually powerless before the violently insane.

That was the theory, anyway. In practice, as that old-timey police captain well knew, coercion — jail — was applied because “therapy” was non-existent and, anyway, a prescription for continued mayhem.

Then came the progressive “reforms” of 2019. Now hardly anyone goes to jail for anything — and the thoroughly predictable result has been a sharp rise in seemingly motiveless violent crime.

Except they’re usually not motiveless at all — but rather driven by demons that defy reason, let alone compassionate understanding. They’re just invisible.

None of this makes any difference to the city’s growing league of random victims — babies in strollers, wide-eyed tourists, elderly straphangers and, Tuesday morning, Brooklyn commuters.

Who speaks for them? Who acts for them?

Nobody with the power to help them, that’s for sure.

Kendra’s Law is a well-intentioned half-measure that takes fully into account the interests of the state’s violently insane — but only nominally those of other New Yorkers.

This presumption needs to be flipped on its head. Where interests collide, those of the innocent must prevail — and this, ironically enough, would include those too addled to protect themselves.

Why is this so complicated?

That old cop recognized failure when he saw it. After five decades, you’d think New York would, too.

[email protected]