President Obama’s use of military force in Libya has come under intense criticism across the American political spectrum. There is widespread disagreement over what U.S. objectives should be, and many fault Obama for his initial hesitancy to act, his incoherence in defining our mission, and his ineptness in rallying domestic political support.

The best reason for using force is to secure the removal of Moammar Qaddafi. Even that objective has its complications, not least the question of what kind of regime will succeed him. But Qaddafi’s declared intention and demonstrated capacity to return to international terrorism, and the risk he would likewise resume his pursuit of nuclear weapons, fully justify removing him from the scene.

But this is not why our president ordered U.S. forces into action. His rationale, explicitly articulated in Security Council Resolution 1973, is protecting Libyan civilians. While that strikes many as praiseworthy, others ask how it can be fully realized without removing Qaddafi.

In fact, Obama is pursuing ideological, not geopolitical, objectives. He said in Chile on March 21 that “the core principle that has to be upheld here is that when the entire international community almost unanimously says that there’s a potential humanitarian crisis about to take place, that a leader who has lost his legitimacy decides to turn his military on his own people, that we can’t simply stand by with empty words, that we have to take some sort of action.”

Obama’s comment is a paradigmatic statement of the beguilingly known “responsibility to protect,” a gauzy, limitless doctrine without any anchor in U.S. national interests. This putative responsibility emanates from the desire to divert American military power from protecting U.S. interests to achieving “humanitarian” objectives. The doctrine had its adherents even in the Bush administration, but they have reached measurable power only now under President Obama. The current U.S. military engagement in Libya, as he has defined it, is the jewel in their crown.

The “responsibility to protect,” of course, is limitless by its own terms. Why are we not using force to protect the North Koreans, who’ve suffered through decades of totalitarian rule? Why are we not using force to protect Zimbabweans from Robert Mugabe, whose abuses are easily on a par with Qaddafi’s? What about Syrians, Iranians, Tibetans, etc.?

The endlessness of the responsibility to protect is not a conceptual problem with the doctrine, but its essence. It cannot be “corrected,” because that is its core message. And its error lies not just in its unbounded vistas, but in its critical dirty secret among the international High-Minded: It requires using someone else’s troops, usually ours, to achieve moral satisfaction. President Obama revealed this acutely troublesome aspect when he said recently: “It means that we have confidence that we are not going in alone, and it is our military that is being volunteered by others to carry out missions that are important not only to us, but are important internationally.” Having our military “volunteered” by others is easy for those doing the volunteering, but potentially fatal for the honorees. Having an American president willingly adopt this expansive view of our military’s legitimate purposes is no answer to the basic question of why their lives are being risked. These are unquestionably rationales disconnected from U.S. national interests, and a disconnected president does not bridge the fundamental disjunction.

Advocates of the doctrine respond that military force is only one aspect of a broader theory, but force is inevitably central to any debate about humanitarian intervention. Providing food to a war’s starving victims in a permissive environment is something Americans do instinctively; sending their sons and daughters into conflicts that do not affect their vital interests is something else altogether. Moreover, the “responsibility to protect” is not just another euphemism for U.N.-style peacekeeping. Successful peacekeeping operations rest on the consent of the parties to the conflict in question, which obviates any reason for the “protectors” to use force, and dramatically reduces any risks even in providing humanitarian assistance.

In addition, while the “responsibility to protect” seems to present an alluring moral clarity, it dangerously ignores competing moral claims. The highest moral duty of a U.S. president, for example, is protecting American lives, and casually sacrificing them to someone else’s interests is hardly justifiable. Imagining a future tragedy of Holocaust-sized dimensions and asking whether we would stand idle even in its face may tug at our heartstrings, but emotion is not a policy. And let us be clear: Even the real Holocaust did not motivate U.S. war planners from Franklin Roosevelt on down. They remained entirely focused on the military destruction of Nazi Germany.

Some “responsibility” advocates, conceding that their doctrine obviously cannot be applied universally, argue we should at least act in “easier” cases. Thus, they say, while the risks and costs of protecting the people of North Korea or Iran may be too great, instances such as Libya do not pose nearly such grave challenges. This analysis implicitly assumes that assessing the cost-benefit ratio prior to a humanitarian military mission is relatively straightforward. If only this were so.

Painful experience proves that what initially seems uncomplicated can quickly become mortally complicated. As Churchill put it, “Never, never, never believe any war will be smooth and easy.” Once war is launched, a combatant “is no longer the master of policy but the slave of unforeseeable and uncontrollable events.” This is as true of “protection” missions as it is of regime-change invasions.

Almost inevitably, a military intervention alters the balance of forces in a conflict, advantaging one set of combatants over another. Protecting some will likely mean death for others. In Libya, for example, we might prefer to think we are simply opposing Qaddafi and not “siding” with the opposition, but effectively we are doing just that. And are all Qaddafi’s adherents, and he has many, as guilty as he for his crimes and deserving of the same treatment? Equally invariably, the disadvantaged side will not take kindly to being intervened against. Terrorist and guerrilla tactics kill humanitarians just as dead as imperialists.

And, as in Somalia, there are no guarantees that the Libyan opposition will not turn out to be as brutal as the ruler it replaces. What do we do then? Police both sides? And what if there are more than two sides, and all of them come to oppose international intervention? At least where there are American interests at stake, there are metrics with which to do our analysis.

And the problems of withdrawal or “exit strategy” are not necessarily less complex in humanitarian interventions than in regime-change invasions such as those in Iraq and Afghanistan — the length and human cost of which have been criticized by many of the leading advocates of the responsibility to protect. Take Rwanda: When would a responsibility-to-protect force have known it was safe to leave Hutus and Tutsis alone together?

The Clinton administration experienced precisely this problem in Somalia, taking a limited Bush 41-administration effort to open humanitarian-relief channels, turning it into an exercise in nation building, and ending the operation in failure after the death of 18 service members in Mogadishu. Clinton-administration policy in Somalia is perhaps the closest parallel to the current situation in Libya: It looked easy, and it turned into a humiliating debacle for America and its president. Let’s be blunt. The question comes down to this in every case: How many dead Americans is it worth to you?

The doctrine’s political vagueness is as troubling as its limitlessness. Which nations, for example, constitute the “international community” that determines the existence of the responsibility to protect? While Obama said that, for Libya, this community was almost unanimous, five of 15 Security Council members abstained on Resolution 1973, which implemented the “duty.” The five abstainers included Russia and China — no surprises there. But they also included India, Brazil, and Germany, which at last report were all at least somewhat free and democratic. Moreover, by speaking of a “potential” humanitarian crisis, the president justified the preemptive use of force, a point worth noting given his criticism of prior administrations for precisely that.

Libya will be a most interesting test case, whether Qaddafi stays or goes, and, if he goes, whoever replaces him. In the happy event that Qaddafi either flees Libya or is killed, the doctrine’s advocates will claim success, foreshadowing subsequent missions. They will be wrong but lucky, which may, unfortunately, be more important in their impact on future U.S. foreign policy. If the international Lord Protectors remain in command at the White House, more Libyas will ensue.

The question now, therefore, is whether the American people agree. We should have a national debate on the “responsibility to protect.” Congress should discuss whether committing our young service members, at risk of life and limb, for purely “humanitarian” reasons, is legitimate national policy. We can admire the intentions of those who adhere to the doctrine, but we should ask respectfully whether they truly understand the consequences of their morality. And we should say to them unambiguously: If you want to engage in humanitarian intervention, do it with your own sons and daughters, not with ours.

Mr. Bolton, a former U.S. representative to the United Nations, is a senior fellow at the American Enterprise Institute.

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