Animals are endued with a capability of perceiving pleasure and pain; and from the abundant provision which we perceive in the world for the gratific… - Thomas Young (animal welfare writer)

A man who has made a tolerable progress in humanity, will adopt, and ever bear in mind, the principle of increasing, as far as lies within his power, the quantity of pleasure in the world, and diminishing that of pain: he will establish this to himself as a constant and inviolable rule of action, and in carrying it into practice he will not overlook one created thing that is endowed with faculties capable of perceiving pleasure and pain. He will reflect on who it was that gave these faculties and remember that they were not given to be sported with. He will not esteem the meanest of animals beneath the notice of his humanity because, in the meanest of them, the wisdom and power of the all-benevolent Being are displayed. This is the Being without whom not a single sparrow shall fall to the ground and whose bounty feeds the young ravens that call upon him. His sensibility will be tremblingly alive to the sensations of all animated nature, and he will feel for everything that is capable of feeling: he will look upon pity, kindness, and mercy toward his own species as the weightier matters of humanity, but at the same time, he will consider the humane treatment of animals as more than the tithe of the anise and cummin of it. He will scrupulously do his duty in the former, and in the latter, he will not leave it undone.

Every single act of cruelty contributes something towards generating in the mind an habit of cruelty.

[E]very experiment is cruel which gives pain to an animal, without having for its object the leading to some great and public good.