The entire cash-on-a-pallet debate about the $400 million payment the U.S. made to Iran in January rests on a single assumption: that paying ransom for hostages is a bad thing. But it isn't, at least not always.

All negotiations and transactions depend on leverage. Hostages are a form of leverage, and so is money. So is military force. Frequently, paying ransom is the least expensive and most effective way to achieve the goal of recovering hostages.

And on close reflection, ransom payments don't really create new incentives for bad actors to take hostages — because those incentives already exist, and can't be eliminated by insisting that paying ransom is something the U.S. will never do.

Why does a country like Iran take hostages in the first place? Simply put, it's trying to get vastly stronger actors, like the U.S., to do what it wants. In this way, a hostage-taking country is not so different from a brigand in an unpoliced area who takes hostages as a moneymaking venture. The kidnapper is exploiting two vulnerabilities.

First, the kidnapper can get hold of a person who is unprotected, and can't easily be caught without the hostage being harmed. Second, the hostage wants to live freely — and the hostage's friends and family want the same thing for him or her.

There are really only two ways to eliminate hostage-taking, and they correspond to the two vulnerabilities.

One is not to get grabbed in the first place. That isn't very realistic for all Americans, who travel freely around the globe and sometimes make themselves vulnerable to capture.

The other is not to care about the hostage being taken at all. At the personal level, that requires both hostages and their friends and family to be prepared to accept indefinite or even permanent detention. Understandably, that's extremely rare.

At the national level, not caring would require a broadly shared political value that accepts the detention or death of Americans as the price we all pay for our freedom to travel and our nation's global power. Such a Spartan view isn't realistic in our democracy, and I'm not sure it would be ethically desirable even if it were.

The upshot is that American hostages will inevitably be taken, and Americans, including some in the government, will inevitably want to get them back.

The question, then, is whether it's a sensible principle for the U.S. never to pay ransom to do so.

Here the answer is an unequivocal no. The alternative to paying ransom is to use economic sanctions or to threaten force. Those are both good tools of foreign policy, but both are blunt instruments rather than scalpels.

Economic sanctions harm an entire country or industry, and are also often costly to those who impose them.

Force could be directed specifically at recovering particular hostages, but as President Jimmy Carter's failed attempt should remind us, it's hard to execute. Other forms of force may kill innocent bystanders or otherwise strengthen anti-American sentiment.

In contrast, paying ransom is the simplest and most direct way to get back hostages, presuming you want them returned.

But what about the incentive it creates for more hostage-taking? My Bloomberg View colleague Eli Lake points out that "when it comes to Iran, ransom payments are standard operating procedure" — a statement that is 100 percent true. And he adds that the Iranians have learned that hostage-taking works — which is also perfectly accurate.

But Iran didn't need the U.S. to teach it that hostage-taking is effective. The incentive to take hostages is immediately obvious to anyone trying to gain leverage over a more powerful actor. There's a reason hostage-taking is as old as recorded history.

And that's why it's a bit absurd to think that the U.S. should never pay ransom — because refusing to pay ransom will make it much harder to get back hostages without eliminating the incentive to take them in the first place.

It sounds tough to say that we don't pay ransom. But we do; we have; and we will — so long as we care about our citizens, and so long as humans are willing to use other humans as leverage to accomplish their goals.

Noah Feldman, a Bloomberg View columnist, is a professor of constitutional and international law at Harvard.