Libertarian Reasons Against War (in no particular order):
1. War requires aggression.
It’s simply irresponsible to speak of war without innocent casualties. Given the weapons, tactics, and scale of modern warfare, civilians are inevitably put in harm’s way. To separate modern warfare from innocent deaths seems to rely on an unrealistic conception of how war actually is in the real world. The notion of “defensive war” is long outdated. All wars are aggressive. Even ones that are supposedly fought in response to some sort of aggression end up killing innocents.
But what if those civilian casualties are merely a side-effect of defending against an aggressor, the actual goal of so-called defensive war? The killer didn’t mean to kill those people. They died as an unintended consequence of the war. Simple collateral damage. Well so what? The killer knew innocent deaths would be an unintended consequence of their decision to pursue war with near absolute certainty. They actively took steps that would result in the foreseen deaths of innocents, even if their other ends were good. If I shoot at a crowd of ten people because I think one of them stole my wallet, any deaths are still my fault even if I was just trying to stop the person who took my wallet. I caused those deaths. Good intentions don’t justify ignoring known, but unintended consequences. Wanting nice things doesn’t grand one a license to pursue mass murder.
But suppose that the would-be killer didn’t know that civilians were going to die because of his actions. Again, so what? Aggression doesn’t always involve moral culpability. We can still say the act of war was wrong in hindsight because of the innocent deaths and that the aggressor owes restitution to the victim or their family and friends. If I’m shooting at a thief who stole my wallet and one of the bullets ricochets and kills someone else completely away from the incident, it doesn’t look like I’m morally culpable for that person’s death. I didn’t know my actions would have that result so how could I be guilty? Nonetheless, I’m responsible for the instance of aggression and owe them or their loved ones restitution. Ignorance is also not a justification for mass murder.
War inevitably rests on aggression. Conflicts of international scale with the technology and weaponry available in today’s world cannot escape civilian deaths and other instances of aggression against innocent people. Therefore, there is no such thing as a war of self-defense. If force is only to be permitted in self-defense, war is unacceptable.
In addition to the above, war also relies on taxation and monopoly, which are sustained through systematic government violence. The institutional factors that give rise to war are themselves based on one group (the government) warring against another (the citizens). War, then, is an example of evil means and evil ends.
2. War makes everyone less safe.
War causes blowback. War naturally creates ideological and emotional conflict between the people of the warring regions. With every blow, more and more people of the targeted region (often innocent civilians suffering due to a sanction or other forms of economic terrorism, or worse, the loss of a loved one due to a bombing or other forms of military violence) are incentivized to deliver a blow back to the aggressor for reasons often completely unrelated to the initial conflict, such as self-interested defense, hostile revenge, or even newly sparked nationalism. These victims then often turn to militaries or their own cooperative efforts to carry out their blowback. The initial attack, even if motivated by self-defense, inadvertently caused innocent victims, and more and/or increased threats to the attacker.
War, then, escalates conflict. War is a never-ending circle of violence, continually sowing the seeds for more war. Both sides take turns delivering punches to the other, each one more powerful than the last. Neither region ever benefits since even the attacking region lays the ideological foundations for its doom. Even so-called “victorious” attacks are merely temporary victories. They achieve a short-term loss, but create more hostility, hate, and eventually violence than the attack stopped. War leads to blowback, which leads to more war, which leads to more blowback, and so on. The unintended consequences and side effects of war make each region less safe as it only feeds into more violence, hatred, bigotry, and, well…war. Each region becomes increasingly less safe until one side finally crushes the other for good (usually paving the way for further conflicts and wars) or they both collapse.
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Full article here.