An obvious implication is that political ethics, originally identical with the ethics of war, must long remain akin to them; and can diverge from them only as warlike activities and preparations become less. Current evidence shows this. At present on the Continent, the citizen is free only when his services as a soldier are not demanded; and during the rest of his life he is largely enslaved in supporting the military organization. Even among ourselves a serious war would, by the necessitated conscription, suspend the liberties of large numbers and trench on the liberties of the rest, by taking from them through taxes whatever supplies were needed—that is, forcing them to labour so many days more for the State. Inevitably the established code of conduct in the dealings of Governments with citizens, must be allied to their code of conduct in their dealings with one another.
– Herbert Spencer, “The Sins of Legislators”
This is the single best argument against war I have ever seen.