The Hindu custom of "Suttee," in which a widow was burned alive... sometime voluntarily, and often not.
In recent times we are often told that all cultures are equal, and that one should not suggest that one culture is superior to another. However, the following story both shows the folly of this view, as well as how those of the old school handled cultural diversity.
In the mid 1800's, when Britain ruled India, they banned the custom of burning widows alive on the funeral pyres of their husbands. A delegation of Indians came to Sir Charles James Napier, to complain that this was their ancient custom, and that they should be allowed to practice it.
This was Sir Charles' response:
"You say that it is your custom to burn widows. Very well. We also have a custom: when men burn a woman alive, we tie a rope around their necks and we hang them. Build your funeral pyre; beside it, my carpenters will build a gallows. You may follow your custom. And then we will follow ours."
For the most part, this custom died out.
Sir Charles James Napier