The Theory of Moral Sentiments by Adam Smith

Since our sentiments concerning beauty of every kind, are so much influenced by custom and fashion, it cannot be expected, that those, concerning the beauty of conduct, should be entirely exempted from the dominion of those principles. Their influence here, however, seems to be much less than it is everywhere else. There is, perhaps, no form of external objects, how absurd and fantastical soever, to which custom will not reconcile us, or which fashion will not render even agreeable. But the characters and conduct of a Nero, or a Claudius, are what no custom will ever reconcile us to, what no fashion will ever render agreeable; but the one will always be the object of dread and hatred; the other of scorn and derision. The principles of the imagination, upon which our sense of beauty depends, are of a very nice and delicate nature, and may easily be altered by habit and education: but the sentiments of moral approbation and disapprobation, are founded on the strongest and most vigorous passions of human nature; and though they may be warped, cannot be entirely perverted.

But though the influence of custom and fashion upon moral sentiments, is not altogether so great, it is however perfectly similar to what it is everywhere else. When custom and fashion coincide with the natural principles of right and wrong, they heighten the delicacy of our sentiments, and increase our abhorrence for everything which approaches to evil. Those who have been educated in what is really good company, not in what is commonly called such, who have been accustomed to see nothing in the persons whom they esteemed and lived with, but justice, modesty, humanity, and good order; are more shocked with whatever seems to be inconsistent with the rules which those virtues prescribe. Those, on the contrary, who have had the misfortune to be brought up amidst violence, licentiousness, falsehood, and injustice, lose, though not all sense of the impropriety of such conduct, yet all sense of its dreadful enormity, or of the vengeance and punishment due to it. They have been familiarized with it from their infancy, custom has rendered it habitual to them, and they are very apt to regard it as, what is called, the way of the world, something which either may, or must be practised, to hinder us from being made the dupes of our own integrity.