Sometimes expediency and right (as we understand the terms) will appear to clash. In order to avoid mistaken decisions when this happens, we must establish some rule to guide us in making such comparisons and to prevent us from deserting our obligations. That rule will be in accordance with the teaching and system of the Stoics; they are my models in this work - for the New Academy (to which I belong) gives us wide latitude to support any theory which has probability on its side. But to return to my rule.
Well, then, to take something away from someone else - that one man should profit by another's loss - is more unnatural than death, or destitution, or pain, or any other physical or external blow. To begin with, it strikes at the roots of human society and fellowship. For if we each of us propose to rob or injure one another for our personal gain, then we are clearly going to demolish what is more completely natural than anything else in the world: the link that unites every human being with every other. Just imagine if each of our limbs had its own consciousness and decided it would do better if it appropriated the nearest limb's strength! Of course the whole body would inevitably collapse and die. In precisely thc same way, if every one of us seizes and appropriates other people's property, the human community, the brotherhood of mankind, collapses. It is natural enough for a man to prefer earning a living for himself rather than for someone else - granted; but what nature forbids is that we should increase our means, property and resources by plundering others.
Indeed this idea - that one must not injure anybody else for one's own advantage - is not only natural law, an internationally valid principle; it is also incorporated in the statutes which individual communities have framed for their national purposes. The whole point and intention of those statutes is that one citizen shall live safely with another: anyone who attempts to undermine that association is punished with fines, imprisonment, exile, or death.
The same conclusion follows even more forcibly from the rational principle in nature, the law that governs gods and men alike. Whoever obeys it - and everyone who wants to live according to nature's laws must obey it - will never be guilty of coveting another man's goods or appropriating for himself what he has taken from someone else. For great-heartedness and loftiness of soul, and courtesy, and justice, and generosity, are far more natural than self-indulgence, or wealth, or even life itself. But to despise this latter category of things, to attach no importance to them in comparison with the common good, really does need a great and lofty heart.
In the same way, it is more truly natural to model oneself on Hercules and undergo the most terrible labours and troubles to help and save all the nations of the earth than (however superior you are in looks or strength) to live a secluded, untroubled life with plenty of money and pleasures. Mankind was grateful to Hercules for his services, and popular belief gave him a place among the gods.
So the finest and noblest characters prefer a life of dedication to a life of self-indulgence: and one may go further, and conclude that such men conform with nature (for that is just what they do) and will therefore do no harm to their fellow-men.
In conclusion: a man who wrongs another for his own benefit either imagines, presumably, that he is not doing anything unnatural, or he does not agree that death, destitution, pain, the loss of children, relations, friends, are less deplorable than doing wrong to another person. But if he sees nothing unnatural in wronging a fellow-being, how can you argue with him? - be is taking away from man all that makes him man. If, however, he concedes tbat this ought to be avoided, but regards death, destitution, and pain as even more undesirable, he is mistaken in believing that any damage, either to his person or to his property, is worse than a moral failure.
So everyone ought to have the same purpose: to make the interest of each the same as the interest of all. For if men grab for themselves, it will mean the complete collapse of human society.
And if Nature prescribes (as she does) that every human being must help every other human being, whoever he is, just precisely because they are all human beings, then - by the same authority - all men have identical interests. Having identical interests means that we are all subject to one and the same Law of Nature: and, that being so, the very least that such a law must enjoin is that we may not wrong one another. The hypothesis of that proposition is true; so the conclusion is true also. People are not talking sense if they claim (as they sometimes do) that they do not intend to rob their parents or brothers for their own gain, but that robbing their other compatriots is a different matter. That is the same as denying any common interest with their fellow-countrymen, or any consequent legal or social obligations. And such a denial shatters the whole fabric of national life.
Michael Grant, ed., Latin Literature, An Anthology, London, 1989, 34-36.