I was relating to my daughter a story by Chrétien de Troyes called "Lancelot, the Knight of the Cart". It gets its name from when Lancelot is pursuing Guinevere and her kidnapper. Having ridden two horses to death, he hitches a ride with a dwarf driving a cart. Even in the twelfth century, Chrétien could not expect his audience to understand about knights and carts; as he explains at length, it was a great disgrace for anyone to ride in a cart, and especially a knight:
…the people are greatly amazed to see the knight borne upon the cart, and they take no pains to conceal their feelings, but small and great and old and young shout taunts at him in the streets, so that the knight hears many vile and scornful words at his expense. They all inquire: "To what punishment is this knight to be consigned? Is he to be rayed, or hanged, or drowned, or burned upon a fire of thorns? Tell us, thou dwarf, who art driving him, in what crime was he caught? Is he convicted of robbery? Is he a murderer, or a criminal?"
The whole business is frankly baffling to a modern mind — which is exactly why you should read it, and old books in general: in them, you will find all the evidence you could ever need of the changeability of human judgment. Old books frequently approve what we condemn and revile what we embrace. They disagree with each other on details, yes, but even on foundational matters: how should we view the world and our rôle in it? They cannot agree even there! The reader is forced to confront the question: if the ancients cannot agree even with the slightly less-ancients, and both disagree with us at every turn, how can we be certain that we, in our enlightened age, have finally arrived at correct opinions on all these matters?
If we cannot be sure our society's consensus on any matter is correct and definitive, how can we force conformity in opinion and practice? We have to leave room for disagreement and debate, room for diversity of opinion: that is, we must lay the foundation of liberty, which is tolerance.