A free society must always be vigilant in watching its guardians.

But that doesn’t mean a free society can do without guardians in the first place.

Those are the proper starting points from which to judge President Obama’s speech at the Justice Department Friday morning. The modest moves he announced to reform the data-gathering and surveillance practices of the federal government’s sprawling national security infrastructure should be welcomed — as should his effort to share responsibility with Congress for the controversial programs.

But we should also be grateful that the president didn’t go further in dismantling them.

The disturbing fact is that in the months since Edward Snowden and his megaphone Glenn Greenwald first became civil libertarian folk heroes, there has been a been a precipitous rise in self-righteous silly talk in the U.S. and abroad about the ominous threats posed by the very act of government surveillance.

Sure, it would be wonderful if we didn’t live in a world in which people plotted to kill as many Americans as possible. But we don’t live in that imaginary world. In the world we do live in, there are many such plots, as well as weapons with which those individuals could potentially kill many thousands of Americans.

How great are these threats? This is certainly a matter of dispute. But even though the efficacy of the NSA's spying program is in question, it's still eminently reasonable and morally defensible for the president to exploit this tool to its fullest extent within the law. Acting otherwise would be a monumental act of irresponsibility.

This is something Obama himself (like many past presidents) has grudgingly come to understand.

Let’s call it the Raymond Aron lesson. One of the wisest political minds of postwar Europe, Aron spent quite a lot of time embroiled in clashes with unwise intellectuals and journalists who were fond of issuing grandiloquent (and self-aggrandizing) denunciations of the manifest moral failings of those in political power.

Of course it’s perfectly acceptable — indeed essential for the healthy functioning of a liberal democracy — for intellectuals and journalists to criticize politicians, sometimes strenuously. But the behavior of Parisian intellectuals and journalists in Aron's case was something different: A wholesale condemnation of governing and the responsibilities that go along with it. This included the responsibility to defend the common good, sometimes with tactics that fall short of the moral purity we might expect of a private individual.

That’s why Aron made a simple suggestion: Those who write about and comment on politics ought to constantly ask themselves: "If you were in the minister’s position, what would you do?" It was an effort to get these critics to think deeply about the burdens of political responsibility.

Barack Obama has learned the Raymond Aron lesson — that it’s easy to take pot shots at those in power when you’re responsible for no one’s good but your own. The world looks much different when the safety and well-being of a nation of 313 million people is at stake in every decision.

Whether Obama’s most vociferous critics will ever learn this lesson remains to be seen. If they don’t, it will be because of a failure of political imagination — of a refusal to place themselves realistically in the president’s position.

If he ever literally found himself in President Obama’s position, even Glenn Greenwald would endorse NSA spying.