I didn't know this about the Shelleys (Percy Bysshe and wife Mary, who wrote Frankenstein)
From Wikipedia- "Vegetarianism
Both Percy Bysshe and Mary Shelley were strong advocates of vegetarianism. Shelley wrote several essays on the subject, the most prominent of which being "A Vindication of Natural Diet" and "On the Vegetable System of Diet".
Shelley, in heartfelt dedication to sentient beings, wrote: "If the use of animal food be, in consequence, subversive to the peace of human society, how unwarrantable is the injustice and the 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"; "Never again may blood of bird or beast/ Stain with its venomous stream a human feast,/ To the pure skies in accusation steaming"; and "It is only by softening and disguising dead flesh by culinary preparation that it is rendered susceptible of mastication or digestion, and that the sight of its bloody juices and raw horror does not excite intolerable loathing and disgust."
Shelley was a strong advocate for social justice for the 'lower classes'. He witnessed many of the same mistreatments occurring in the domestication and slaughtering of animals, and he became a fighter for the rights of all living creatures that he saw being treated unjustly."