To be effective, morality has to be reasoned (or worked out). To want ("vouloir", Fr.) to repress evil only by coercion, and to obtain morality by a sort of training with the help of constraint, without motivating it from within, is to make it an unnatural result, devoided of lastind value.
Free speech carries with it the evil of all foolish, unpleasant venomous things that are said but, on the whole, we would rather lump them than do away with them.
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.
How great an evil do you see that may have been announced by you against the Republic? - Videtis quantum scelus contra rem publicam vobis nuntiatum sit?
Evil is the radiation of the human consciousness in certain transitional positions. It is not actually the sensual world that is amere appearance; what is so is the evil of it, which, admittedly, is what constitutes the sensual world in our eyes.
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.