No form of government has yet been discovered by which cruelty can be wholly prevented. Subordination supposes power on the one part, and subjection on the other, and if power be in the hands of men, it will sometimes be abused. The vigilance of the supreme magistrate may do much, but much will still remain undone. He can never know all the crimes that are committed, and can seldom punish all that he knows. If you haven't read it yet, please read this note of caution regarding quotes from Rasselas.
Laws are often occasional, often capricious, made always by a few, and sometimes by a single voice.