Kwame Anthony Appiah lists three criteria for evaluating whether a current practice will be condemned by future generations:

First, people have already heard the arguments against the practice. The case against slavery didn’t emerge in a blinding moment of moral clarity, for instance; it had been around for centuries.

Second, defenders of the custom tend not to offer moral counterarguments but instead invoke tradition, human nature or necessity. (As in, ‘We’ve always had slaves, and how could we grow cotton without them?’)

And third, supporters engage in what one might call strategic ignorance, avoiding truths that might force them to face the evils in which they’re complicit. Those who ate the sugar or wore the cotton that the slaves grew simply didn’t think about what made those goods possible. That’s why abolitionists sought to direct attention toward the conditions of the Middle Passage, through detailed illustrations of slave ships and horrifying stories of the suffering below decks.

Click on the link to see which four current practices he sees as likely to be condemned in the future.