The butchering of harmless animals cannot fail to produce much of that spirit of insane and hideous exultation in which news of a victory is related altho' purchased by the massacre of a hundred thousand men.
If the use of animal food be, in consequence, subversive to the peace of human society, how unwarrantable is the injustice and barbarity which is exercised toward these miserable victims. They are called into existence by human artifice that they may drag out a short and miserable existence of slavery and disease, that their bodies may be mutilated, their social feelings outraged. It were much better that a sentient being should never have existed, than that it should have existed only to endure unmitigated misery.

"On the Vegetable System of Diet'" (c. 1815; posthumously published, 1929).