You do not settle whether an argument is justified by merely showing that it is of some use. The distinction is not between useful and useless experiments but between barbarous and civilized behaviour. Vivisection is a social evil because if it advances human knowledge, it does so at the expense of human character.
Being against evil doesn't make you good. Tonight I was against it and then I was evil myself. I could feel it coming just like a tide... I just want to destroy them. But when you start taking pleasure in it you are awfully close to the thing you're fighting.
So far as we are human, what we do must be either evil or good: so far as we do evil or good, we are human: and it is better, in a paradoxical way, to do evil than to do nothing: at least we exist.
The contagion of crime is like that of the plague. Criminals collected together corrupt each other. They are worse than ever when, at the termination of their punishment, they return to society.
Man has reason, discrimination and free-will such as it is. The brute has no such thing. It is not a free agent, and knows no distinction between virtue and vice, good and evil. Man, being a free agent, knows these distinctions, and when he follows his higher nature, shows himself far superior to the brute, but when he follows his baser nature can show himself lower than the brute.