It’s been called "ridiculous,” "pointless,” and "one of the most meaningless and truly stupid” benchmarks ever.

In 2014, following Russia’s illegal annexation of Crimea, the NATO allies met in Wales and pledged a number. Member states would "aim to move towards the 2% guideline within a decade.” That is, they promised to spend at least that percentage of their gross domestic product on defense by 2024.

The convoluted and slippery wording — "aim to move toward” — should have been the giveaway. With most of the decade gone, only seven allies honored the pledge last year. That’s more than the three countries that exceeded the benchmark in 2014, but hardly impressive in a club of 30.

That same year, 2022, Russian President Vladimir Putin attacked all of Ukraine and started threatening other countries in the region. And now he’s escalating yet again, by stationing tactical nuclear weapons in his neighboring vassal state, Belarus. So Jens Stoltenberg, the alliance’s secretary general, intends to tweak the stupid, pointless and ridiculous rule at the NATO summit in Vilnius this July. There’ll be no more "aiming” and "moving toward.” Instead, he wants to make 2% "a floor and not a ceiling.”

That raises a question. If 2% was stupid as a ceiling, why would it be less dumb as a floor? Critics of the benchmark say it makes no sense to measure inputs rather than outputs. What NATO wants is martial prowess. What some of its members would get is only more military bureaucracy, or weapons that don’t work with other allies’ hardware, or gear that’s actually useful for NATO’s battle plans.

Besides, why pick a percentage of GDP? Should countries lay off soldiers every time they enter recessions? Greece — which keeps a relatively large army because it’s afraid of fellow NATO member Turkey — has at times topped the 2% only because its economy shrank even faster than its military budget.

Why not instead set the benchmark as, say, an amount per capita? That would propel Luxembourg, which has about 900 soldiers, from 29th place to a respectable 8th, because it’s a rich place with only about 640,000 people. Either way, it’s unlikely that the Grand Duchy — better known for bankers than warriors — will save us from Putin. By the way, one member — Iceland — has no army at all.

Granted, then: The 2% guideline is stupid. To emphasize that, however, is to miss the point. The benchmark’s virtue is that it’s simple. And its necessity derives from the problem it’s meant to address: the massive free-riding by some members on others and on one in particular.

It’s hardly a secret that the trans-Atlantic alliance has the power to deter enemies only because it includes the West’s only superpower. Last year, the U.S. accounted for 70% of NATO’s combined military spending (but "only” 54% of its GDP).

Allies such as Belgium and Portugal have long used this U.S. dominance as a convenient excuse to hide behind the Americans. But the worst offender is surely Germany — because, as NATO’s second-largest economy, it could do so much more. Instead, Germany systematically defunded its army since the Cold War, even as it carried on a recklessly naive dalliance with Putin.

In theory, Putin’s invasion — and nuclear saber-rattling — has now, at long last, snapped the Germans out of their pacific illusions. Last year, Chancellor Olaf Scholz enacted a special defense fund worth €100 billion ($107 billion), meant to top off Germany’s future defense budgets.

In practice, "not a cent arrived” from that fund in 2022, according to Eva Hoegl, the parliamentary commissioner for Germany’s army. She blames the country’s Kafkaesque procurement bureaucracy. In any event, she thinks, the fund would need to be tripled to make a difference. At this rate, she says, it’ll take half a century to get the German army into fighting shape.

In this context, an inane but simple guideline such as the 2% goal becomes a useful political tool. It keeps pressure on laggards such as Germany and simultaneously aids their defense ministers in their domestic sparring with finance ministers and other cabinet members when the budget pie is sliced up. Simultaneously, it helps American legislators make the case to their own constituents that defending Europe is still worth it and that the folks across the pond are paying their share.

In that sense, the 2% guideline resembles other stupid measures that nonetheless make sense once you wrap your mind around the alternative, their absence. Does it make sense for the European Union to arbitrarily stipulate that member states shouldn’t run budget deficits in excess of 3% of GDP or run up debts to more than 60%? Hardly. Unless the EU includes countries, such as Italy, with political and economic cultures that would otherwise abandon thrift entirely.

NATO’s guideline is daft. And I’m glad the alliance has it. Since Putin started imagining he’s Attila the Hun with nukes, we’ve understood that we need to arm to keep him away from us and that we can’t tolerate free-riding in the alliance any longer. Here’s to 2%.

Andreas Kluth is a Bloomberg Opinion columnist covering European politics. He is author of "Hannibal and Me.”