Activists like slogans, and some slogans are accurate, but philosophical positions are often too nuanced to be captured in a bumper-sticker-length slogan.   So in several recent online discussions in which I’ve attempted to explain why Israel is justified in responding to attacks by Hamas, I’ve encountered people saying that because they’re libertarian, they are anti-war, and therefore I must be a bad libertarian.  That’s wrong, and one reason it goes wrong has to do philosophy’s resistance to bumper-sticker sloganeering.

To begin with, saying “war is unjust” is some kind of category error, along the lines of saying “physical force is unjust.”  Wait, the bumper-sticker objects, I thought libertarians were opposed to physical force.  This move elides the moral significance of the distinction between the use of force in aggression and the use of force in defense.  If Bob starts hitting Bill and Bill hits Bob back, they’re both using physical force.  But that doesn’t make them morally equivalent, and this shows why it’s a conceptual mistake to say that “hitting is unjust”: if Bob’s hitting is unjust (aggression), then Bill’s hitting is just (defense).   “Hitting” alone isn’t just or unjust, until we know who is committing aggression, the initiation of force, to violate someone’s rights, and who is using force defensively, to protect their rights.  Libertarianism isn’t about hitting, it’s about rights.  Similarly, saying “war is unjust” misses the important distinction between aggression and defense.  If Sylvania invades Freedonia, say because the former wants to annex the latter to obtain raw materials, Sylvania’s action is unjust.  But that implies that Freedonia’s use of arms to repel the unjust invasion is just.  So the question “is this war just?” is poorly formed.  It’s unjust for the one to have attacked, and (therefore!) just for the other to respond.

Of course, there are complicating variables, so it’s sometimes harder than it first appears to assess justice.  (See my “War and Liberty,” Reason Papers 26, Spring 2006; can’t hyperlink for some reason but it is online.)  But the point I’m making here is that the slogan doesn’t even come close to capturing the variables.   At this point in the argument, someone objects that because there may be harm to innocents, the analogy from Bob and Bill to Sylvania and Freedonia doesn’t work.  But it’s not that the analogy doesn’t work, it’s that there are other factors to be added to the evaluation.  The analogy works in skeletal form – an unjust aggression may be justly opposed – but it’s true that military action carries increased risk of harm to innocents.  This isn’t a particularly novel observation, though, nor is it something that only a libertarian would think of.  It’s been a principle of ethical theory about warfare for centuries.  So it’s true that assessing the morality of a conflict has to involve the degree to which both parties take care to minimize harm to noncombatants.  But here too, the moral assessment is not unitary: if Sylvania is indiscriminate in attacking but Freedonia avoids targeting civilians, we’d say “Sylvania is fighting unjustly” and also “Freedonia is fighting justly.”

Another objection that is largely a red herring is to note that it’s states that go to war, and the fighting is thus subsidized by involuntarily-collected taxes.  I certainly agree that states shouldn’t do this.   But not everything that a state does is illegitimate per se.  There are state activities that would be morally legitimate if not done by the state, so it’s only that the state is doing them that makes them bad.  If it’s already bad, then it’s bad for the state to do it (for example, private citizens owning slaves is morally wrong, so for the state to enslave people is also wrong).  But if it’s morally permissible to do a thing, then the wrongness of the state doing it comes from libertarian objections about the nature of state activity.  For example, the occupation of firefighter is morally legitimate, so to complain about state-run fire departments is not to object to firefighting per se, but to the scope of state power.  (See also: teaching.)  So the fact that states engage in macro-level self defense is not wrong because defending yourself is wrong, but because of some theory about the proper scope of state power.  But while we’re arguing about the proper theory of the scope of state power, firefighters are doing a good thing, not a bad thing, when they go put out fires.  And Freedonia’s army is doing a good thing, not a bad thing, when it  repels Sylvania’s invasion.

Sylvania, of course, is doing something wrong: invading Freedonia.  This aggression would be wrong even if it were some non-state entity – it is just like Bob’s attack on Bill.  Bob is wrong to attack Bill.  Sylvania is wrong to invade Freedonia.  Bill is right to fight back; Freedonia is right to fight back.

Now to the extent that the “I’m anti-war” sloganeering is useful, it’s going to be useful in places like Sylvania: making the argument that aggression is unjust, that launching a war is wasteful of resources, that attacks like this are callous about human life.  Libertarians in Sylvania ought to make it clear to their leaders that they oppose the war.  But Freedonians, even libertarian Freedonians, are not bound to say “we should stop fighting”; they have the right to defend themselves.  Remember, just because Bill is a peace-loving person doesn’t mean Bob won’t attack him.  Similarly, a society that eschews aggression may nevertheless find itself attacked.  Some of the people I’ve argued with about this will point out the number of times the US has engaged in warfare that couldn’t plausibly be described as self-defense, as if this were some sort of “gotcha” moment that proves I’m bad at libertarianing.  But this is to confuse history and philosophy.  I’m perfectly aware that the US has acted badly in the past.  But that doesn’t imply that it’s always in the wrong, and more to the point, it doesn’t disprove the normative argument about the legitimacy of self-defense.   So we often end up with something like:
Me: People have a right to defend themselves when attacked.
Other person: Tommy is an aggressive bully.  Carl often starts fights.
Me: ???

Maybe this would fit on a bumper sticker: We should oppose starting wars, but we are not obligated to eschew self-defense.