In the real world in which we live, you always have to choose between evils. And in choosing between evils, you have to have moral criteria for how to make those choices.
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.
Theological religion is the source of all imaginable follies and disturbances. It is the parent of fanaticism and civil discord; it is the enemy of mankind.
When an evil-doer, seeing you practise goodness, comes and maliciously insults you, you should patiently endure it and not feel angry with him, for the evil-doer is insulting himself by trying to insult you.
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.