Does the current interest in “fact-checking” and action to deal with “fake news” serve the cause of better politics? You might think it would, or at least that it couldn’t hurt. I’m skeptical.

The main problem is that teams such as, PolitiFact and the Washington Post’s Fact Checker don’t always do what they say. Often they aren’t checking facts; they’re judging positions or opinions. Testing the opinions of politicians is valuable, of course, if it’s done well. But it isn’t fact-checking — and shouldn’t claim the authority and objectivity that the term implies. Much of the time, this so-called fact-checking is opinion journalism in disguise.

“Barack Obama was born in Hawaii” is the sort of statement a genuine fact-checker checks — a statement that’s simple and precise enough to be either true or false. If you’re checking a claim capable of being “mostly true” or “half true,” or some number of “Pinocchios,” the claim you’re checking isn’t a fact.

Politicians express opinions imprecisely and with phony certitude, giving their declarations the appearance of factual claims. But if their comments can be understood in different ways — their supporters interpreting them one way, their opponents another — they are closer to being meaningless than to being either true or false. This ambiguity accounts for the fact-checkers’ frequent failure to agree. Moreover, slogans such as “climate change is real” or “climate change is a hoax” can’t be properly fact-checked as they stand: In either case, the only intelligent response is, “What do you mean, exactly?” (Admittedly, that wouldn’t be a very promising journalistic franchise.)

Collections of actual or purported facts are of course capable of being “mostly true” or “partly true” in the aggregate. But when facts are arranged to support an opinion, more than aggregation is involved. They’re being plugged into something that’s different in kind.

To decide whether an opinion is well-supported requires not only that you check the stated facts (if any), but that you also consider context, assess underlying assumptions and inspect the logical structure. Missing information, subjective weightings of causal factors, judgments about probabilities and many other confounding influences enter in. Disagreements that mere checking of facts can’t resolve are bound to arise — even before you bring in values, which views about politics generally do.

Hence the expression, difference of opinion.

Predictions — opinions about the future — are especially problematic. Debating his proposed health care reform in October 2008, Barack Obama said that “if you’ve got a health care plan you like, you can keep it.” At the time, as the Wall Street Journal’s James Taranto has pointed out, PolitiFact rated this “True.” In 2009 and 2012, it rated the same statement “Half True.” In 2013, PolitiFact’s “Lie of the Year” was “If you like your health care plan, you can keep it.”

You might say that this sanctimonious intellectual malpractice is of no great consequence: It’s pedantry to complain that fact-checkers don’t appear to know what a fact is, or what a lie is, or what “true” and “false” actually mean. What does it matter, you might ask, if they’re usefully unpacking dubious arguments and helping people to see what stands up and what doesn’t?

One answer is that opinion writers whose shtick is to demand honesty and precision from other people ought to apply that standard to themselves. More important is the harm that comes from sorting contestable opinions into baskets of truth, half-truth and untruth — ruling in effect on what’s legitimate and illegitimate — all under cover of phony objectivity.

The fact-checking outfits, like opinion journalists in general, bring values and biases to the task. The difference is, they deny it, perhaps even to themselves. Then they rule on opinions they disagree with by calling them false or even lies. Useful as the supporting analysis may be, this issuing of certificates of dishonesty — “You’re a liar, and that’s a fact” — is apt to make American politics even more poisonous than it already is.

The traditional distinction between news and opinion is valuable and worth defending. Media companies serve their readers and viewers best if they can be trusted on the facts, state their opinions honestly, and leave people in no doubt about which is which. Today many suppliers of news and comment are attacking the distinction from both sides — setting up as arbiters of true and false for opinions, while declaring that the standard rules for covering hard news in a balanced and disinterested way no longer apply.

They see this no doubt as a public-spirited response to the success of populist politics in the U.S. and Europe, and to the emergence of frighteningly abnormal contenders for power. Yet far from helping to solve the problem — that of political elites disconnected from the concerns and grievances of ordinary voters — they are exemplifying and reinforcing it. If the traditional distinction between news and opinion is no longer tenable, then isn’t everybody in the fake news business? And why would supporters of Donald Trump or Brexit prefer to get their fake news from enemies rather than friends?