I doubt whether men were more virtuous in aristocratic ages than in others; but they were incessantly talking of the beauties of virtue, and its utility was only studied in secret. But since the imagination takes less lofty flights and every man’s thoughts are centred in himself, moralists are alarmed by this idea of self-sacrifice, and they no longer venture to present it to the human mind. They therefore content themselves with inquiring whether the personal advantage of each member of the community does not consist in working for the good of all; and when they have hit upon some point on which private interest and public interest meet and amalgamate, they are eager to bring it into notice. Observations of this kind are gradually multiplied: what was only a single remark becomes a general principle; and it is held as a truth that man serves himself in serving his fellow-creatures, and that his private interest is to do good.

            I have already shown, in several parts of this work, by what means the inhabitants of the United States almost always manage to combine their own advantage with that of their fellow-citizens: my present purpose is to point out the general rule which enables them to do so. In the United States hardly anybody talks of the beauty of virtue; but they maintain that virtue is useful, and prove it every day. The American moralists do not profess that men ought to sacrifice themselves for their fellow-creatures because it is noble to make such sacrifices; but they boldly aver that such sacrifices are as necessary to him who imposes them upon himself, as to him for whose sake they are made….

            The Americans, on the contrary, are fond of explaining almost all the actions of their lives by the principle of interest rightly understood; they show with complacency how an enlightened regard for themselves constantly prompts them to assist each other….

            The principle of interest rightly understood is not a lofty one, but it is clear and sure. It does not aim at mighty objects, but it attains without excessive exertion all those at which it aims. As it lies within the reach of all capacities, every one can without difficulty apprehend and retain it. By its admirable conformity to human weaknesses, it easily obtains great dominion; nor is that dominion precarious, since the principle checks one personal interest by another, and uses, to direct the passions, the very same instrument which excites them.

            The principle of interest rightly understood produces no great acts of self-sacrifice, but it suggests daily small acts of self-denial. By itself it cannot suffice to make a man virtuous, but it disciplines a number of citizens in habits of regularity, temperance, moderation, foresight, self-command; and, if it does not lead men straight to virtue by the will, it gradually draws them in that direction by their habits. If the principle of interest rightly understood were to sway the whole moral world, extraordinary virtues would doubtless be more rare; but I think that gross depravity would then also be less common. The principle of interest rightly understood perhaps prevents some men from rising far above the level of mankind; but a great number of other men, who were falling far below it, are caught and restrained by it. Observe some few individuals, they are lowered by it; survey mankind, it is raised.

Source: The Libertarian Reader, David Boaz