Once, pretty much everywhere, beating your wife and children was regarded as a father's duty, homosexuality was a hanging offense, and waterboarding was approved -- in fact, invented -- by the Catholic Church. Through the middle of the 19th century, the United States and other nations in the Americas condoned plantation slavery. Many of our grandparents were born in states where women were forbidden to vote. And well into the 20th century, lynch mobs in this country stripped, tortured, hanged and burned human beings at picnics.

Looking back at such horrors, it is easy to ask: What were people thinking?

Yet, the chances are that our own descendants will ask the same question, with the same incomprehension, about some of our practices today.

Is there a way to guess which ones? After all, not every disputed institution or practice is destined to be discredited. And it can be hard to distinguish in real time between movements, such as abolition, that will come to represent moral common sense and those, such as prohibition, that will come to seem quaint or misguided. Recall the book-burners of Boston's old Watch and Ward Society or the organizations for the suppression of vice, with their crusades against claret, contraceptives and sexually candid novels.

Still, a look at the past suggests three signs that a particular practice is destined for future condemnation.

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.

With these signs in mind, here are four contenders for future moral condemnation.

Our prison system



We already know that the massive waste of life in our prisons is morally troubling; those who defend the conditions of incarceration usually do so in non-moral terms (citing costs or the administrative difficulty of reforms); and we're inclined to avert our eyes from the details. Check, check and check.

Roughly 1 percent of adults in this country are incarcerated. We have 4 percent of the world's population but 25 percent of its prisoners. No other nation has as large a proportion of its population in prison; even China's rate is less than half of ours. What's more, the majority of our prisoners are non-violent offenders, many of them detained on drug charges. (Whether a country that was truly free would criminalize recreational drug use is a related question worth pondering.)

And the full extent of the punishment prisoners face isn't detailed in any judge's sentence. More than 100,000 inmates suffer sexual abuse, including rape, each year; some contract HIV as a result. Our country holds at least 25,000 prisoners in isolation in so-called supermax facilities, under conditions that many psychologists say amount to torture.