My refusing to eat flesh occasioned an inconveniency, and I was frequently chided for my singularity, but, with this lighter repast, I made the greater progress, for greater clearness of head and quicker comprehension. Flesh eating is unprovoked murder.

The greatness of a nation and its moral progress can be judged by the way its animals are treated.

When a human kills an animal for food, he is neglecting his own hunger for justice. Man prays for mercy, but is unwilling to extend it to others. 

What do they know-all these scholars, all these philosophers, all the leaders of the world - about such as you? They have convinced themselves that man, the worst transgressor of all the species, is the crown of creation. All other creatures were created merely to provide him with food, pelts, to be tormented, exterminated. 

On July 7, 2012, a prominent international group of scientists - cognitive neuroscientists, neuropharmacologists, neurophysiologists, neuroanatomists and computational neuroscientists - gathered at The University of Cambridge to reassess the neurobiological substrates of conscious experience and related behaviors in human and non-human animals. 

The Cambridge Declaration on Consciousness:

The absence of a neocortex does not appear to preclude an organism from experiencing affective states. Convergent evidence indicates that non-human animals have the neuroanatomical, neurochemical, and neurophysiological substrates of conscious states along with the capacity to exhibit intentional behaviors. Consequently, the weight of evidence indicates that humans are not unique in possessing the neurological substrates that generate consciousness. Nonhuman animals, including all mammals and birds, and many other creatures, including octopuses, also possess these neurological substrates.

I'd like everybody to be a vegetarian... In 100 or 200 years time, we may look back on the way we treated animals today as something like we today look back on the way our forefathers treated slaves.

There is no fundamental difference between man and the higher animals in their mental faculties . . . The lower animals, like man, manifestly feel pleasure and pain, happiness, and misery.

But for the sake of some little mouthful of flesh we deprive a soul of the sun and light, and of that proportion of life and time it had been born into the world to enjoy.

Until one has loved an animal, a part of one's soul remains unawakened. 

There is no fundamental difference between man and animals in their ability to feel pleasure and pain, happiness, and misery.