Thomas Aquinas

“ Now it results from one man loving another that he takes no pleasure in the latter's punishment in itself, but only as directed to something else, for instance justice, or the correction of the person punished. ”

“ The unsoundness of mind that excludes the use of reason is opposed to prudence. But that a man who takes pleasure in the punishment of others is said to be of unsound mind, is because he seems on this account to be devoid of the humane feeling which gives rise to clemency.
Art. 4 - Whether clemency and meekness are the greatest virtues? Objection 1: It would seem that clemency and meekness are the greatest virtues. For virtue is deserving of praise chiefly because it directs man to happiness that consists in the knowledge of God. ”

“ As to clemency, it mitigates punishment, not in respect of that which is according to right reason, but as regards that which is according to common law, which is the object of legal justice: yet on account of some particular consideration, it mitigates the punishment, deciding, as it were, that a man is not to be punished any further. ”

“ This moderation of soul comes from a certain sweetness of disposition, whereby a man recoils from anything that may be painful to another. Wherefore Seneca says (De Clementia ii, 3) that "clemency is a certain smoothness of the soul"; for, on the other hand, there would seem to be a certain roughness of soul in one who fears not to pain others. ”

“ Now internal passions are principles of external actions, and are likewise obstacles thereto. Wherefore virtues that moderate passions, to a certain extent, concur towards the same effect as virtues that moderate actions, although they differ specifically. ”