As jaws flap nationwide and tongues cluck disapprovingly in the wake of the Ferguson grand jury’s decision not to indict Police Officer Darren Wilson in the shooting death of Michael Brown, consider this savage irony:

Due to the heroic actions of America’s police officers and police departments over the past two decades, we are now free to have a national debate about the supposedly problematic behavior of America’s police officers and police departments.

That debate doesn’t just involve minorities.

The revolution in policing that swept through the nation in the early 1990s has changed American life so profoundly we can barely remember what it was like in the years when crime was the central domestic preoccupation of the United States.

Consider this: Nearly 100 million people in this country were born after the national crime drop began in 1994.

That means 100 million people think the way we live now is the natural state of things. Most of the rest of us have come to accept it as the “new normal” as well.

This has happened several times in our history. As the late sociologist Eric Monkkonen wrote in his seminal 2001 study, “Murder in New York City,” Americans have often responded to an era of relative calm by deciding that the authorities have been too restrictive and cruel — resulting in a subsequent period in which greater laxity led to higher rates of crime.

Americans today have either never known or have forgotten that that for decades, it was the working theory of police departments that their job was to respond to crimes after they occurred rather than to prevent crime from happening in the first place.

Police departments racked with corruption scandals (like the ones in New York investigated by the Knapp Commission in the 1970s) actually thought it best to keep cops at a bit of a distance from the citizenry, because their interactions were bound to be controversial.

By the early 1990s, Americans (especially those in cities, and especially the poorest among us) were living in a state of near-siege.

So once it was demonstrated that a different approach could actually lower crime and liberate people from their triple-locked homes and Clubbed cars, more aggressive policing became the order of the day.

That day has likely passed. The loosening Monkkonen described has already begun, and will surely continue apace even with the refusal of the grand jury to indict Officer Wilson.

New York City has ended stop-and-frisk, and Police Commissioner Bill Bratton on Tuesday announced a pilot program in which NYPD personnel will wear recording cameras — a trend sure to spread to other departments nationwide.

In addition, Republicans as well as Democrats on Capitol Hill have expressed reservations over the sale of decommissioned US military gear to local police departments, and may well slow or halt the trend in the coming Congress.

“If a conservative is a liberal who’s been mugged,” Tom Wolfe once cracked, “a liberal is a conservative who’s been arrested.”

That joke is probably in need of revision; arrested conservatives are more likely these days to become libertarians — and in fact libertarians are the ones who are leading the fight against militarized policing.

Cops are literal authority figures, and like all authority figures, any civilian encounter with them triggers the possibility that their authority can be abused — or can inadvertently push one’s buttons in a way that dovetails with an ingrained American streak of hostility to authority.

(Check out newly minted Democratic presidential candidate James Webb’s remarkable book, “Born Fighting,” about the “insistent individualism” at the heart of American culture.)

It might surprise Al Sharpton to hear this, but even among white people, it’s rare to find any American who’s only ever had pleasant interchanges with police officers.

Every year, according to the National Highway Traffic Safety Administration, 41 million speeding tickets are written in the United States. The notion that only minorities have infuriating encounters with cops is belied by that astounding factoid.

After all, is there a soul alive who hasn’t reacted negatively (in his heart, at least) to the cop who comes to the driver-side window and asks that obnoxious and oddly schoolmarmish question: “Do you know why I stopped you?”

Cops aren’t merely authority figures. We hire them to put their lives on the line for the rest of us. This is the reason grand juries and juries so rarely take action against them, and surely why the Ferguson grand jury did not indict Wilson.

But make no mistake — if we send police officers the message that it is safer for their careers and reputations to stand down, stand down they will. We are the ones who will have to reckon with the results.