Strangely, America's most painful conversation — the one about race, crime, cops, courts and prisons — could actually provide one of our best opportunities for the nation's left and right to find common ground, or at least a measure of mutual understanding.

But it's an opportunity we find difficult to seize, as we've seen again in the mostly polarized aftermath of grand jury exonerations of cops who killed black suspects in Ferguson, Mo., and on Staten Island in New York.

It's in the context of the deep distress they feel over police violence and soaring incarceration rates that American liberals, and especially African-Americans, most directly confront a truth that is central to the outlook of conservatives and libertarians — at least, in every other context.

It's the truth that governmental power is a fearsome and unruly force that must be closely scrutinized and kept in check.

Big differences exist in the kinds of government coercion we're talking about here. Conservatives and libertarians most often decry the burdens of taxation and regulation, the meddlesome social engineering of planners, the activism of courts, and the imposition of Washington's will on states and localities.

Meanwhile, on the streets of poor and minority neighborhoods, government agents "regulate" with nightsticks and handguns.

On the other hand, conservatives might argue that some impositions on liberty simply are more necessary than others. Maintaining law and order, combating crime, is imperative — indispensable precisely for the crime-ridden neighborhoods where relations with police are often the most tense.

We may have no choice, in other words, but to give cops enough discretion to confront and apprehend lawbreakers as they, within reason, deem necessary. But is it equally justifiable for citizens to be (bloodlessly) pushed around to serve every social and economic vision of policy elites?

The point is that the essential dilemma is the same. We need cops and courts and prisons — and we need taxation, regulations, planning and safety-net programs. But wherever there is power there is also the temptation to excess and abuse.

Spotting this common thread of anxiety about "big government" might give our estranged factions a wispy connection to build upon.

Conservatives sometimes seem too quick to discount the broad complaint that (in effect, if not design) a kind of oppressive police occupation has descended on many minority neighborhoods as a result of America's crackdown on crime over the past quarter-century or so — with its painful incarceration levels, its aggressive "broken windows" police tactics, the war on drugs, etc.

Part of the trouble is that this issue often arises most forcefully, as in Ferguson and New York, in connection with specific allegations against individual cops. The officers in such cases are instantly transformed from enforcers wielding the terrible power of the criminal justice system to defendants at the mercy of that power.

Given what we expect of them, cops in these situations deserve (as these received) every reasonable benefit of the doubt — and above all a painstaking examination of the facts of their cases, without reference to "larger issues" that are irrelevant to their individual guilt or innocence.

But the effect of all this is that cops largely do — and really must — operate on our streets with a level of impunity. Can any conservative or libertarian — believing, as one supposes they do, in the universal corrupting effect of unchecked power — doubt the inherent dangers of that reality, especially when coupled with our era's get-tough-on-crime turn in the law and in social attitudes?

Crime, as I recently celebrated on these pages, has plummeted in recent decades. How much aggressive policing and the prison boom have contributed to that is uncertain, researchers say. But even assuming that they have helped, conservatives ought to be quite comfortable, on their own principles, with a conversation about whether the crime crackdown has gone too far, and whether more needs to be done to hold abusive cops accountable and get them off our streets — perhaps through reformed disciplinary rules rather than the criminal justice system.

Heavy-handed cops are surely one vivid kind of big government run amok.

It is frankly harder to be hopeful that liberals could gain much respect for the right's concerns about government excesses, not least because the economic, social and even religious freedoms often said to be endangered by the progressive agenda are not matters of life and death.

Besides, an unshakable confidence that the progressive agenda is so inspired that it should be mandatory — right down to the contents of school lunch menus — seems almost to be what defines progressivism.

And yet, perhaps on the left, too, the anguish on our city streets could serve as a reminder that all exercise of government's coercive power — however well-intended and beneficial on the whole — can drift out of control and become oppression. Thus it all needs to be kept in check and in balance.

The revelations of the Senate torture report are of course just another reminder of arbitrary government action gone wrong. They point in turn to the real significance of debates over presidents exceeding their proper powers. Whatever powers the office secures will one day be in other hands.

All voices do need to be heard, in all disputes. And all liberties, like all lives, matter.

D.J. Tice is at Doug.Tice@startribune.com.