Seneca the Younger Quote

Deeds that would be punished by loss of life when committed in secret, are praised by us because uniformed generals have carried them out. Man, naturally the gentlest class of being, is not ashamed to revel in the blood of others, to wage war, and to entrust the waging of war to his sons, when even dumb beasts and wild beasts keep the peace with one another. Against this overmastering and widespread madness philosophy has become a matter of greater effort, and has taken on strength in proportion to the strength which is gained by the opposition forces.

Letter XCV - Epistulae Morales ad Lucilium (Moral Letters to Lucilius)