The other day I was leafing through some old family papers, and I came across a document that showed that one of my distant ancestors owned a slave.

It was an unsettling moment, for reasons which you can probably guess. I felt sadness. Embarrassment. Shame at having that kind of mark on our family tree. I looked through more records and, fortunately, didn't find anything else like that. However, I wondered about my other ancestors who lived during that same time. Maybe they didn't own slaves themselves, but how did they go about their daily lives knowing that the enslavement of their fellow human beings was going on all around them? Why aren't their names in the history books as vocal abolitionists who refused to rest until justice reigned in their land? I shook my head, said a prayer for the souls of everyone involved, and put the document away.

Then, a few moments later, another reaction hit me, this one more immediate and unsettling than the one before.

When I had first seen the note that included a human being among my ancestor's possessions, I was consoled by a sense of distance: Yes, it was terrible that it happened, but at least we, as a society, learned our lesson from the whole sordid situation. At least I can take comfort in the fact that I would never be involved in anything like that.

But the delayed realization that hit me like a punch in the gut was the dreadful question: Am I so sure that I would have done anything differently?

We all want to believe that if we'd lived in 1712 instead of 2012, we'd have been tireless abolitionists. It's comforting to tell myself that if I lived in Nazi Germany I would have worked to thwart the despicable plans of Hitler's regime. If I were a Hutu in Rwanda in the 1990s, surely I would done all that I could to aid my Tutsi neighbors. If I lived in pagan Rome I just know I would have raged against the practice of abandoning unwanted infants to die alone.

But the review of those old family documents stripped all those assuring thoughts away, and left me with the stark awareness that people ignore great injustice all the time. In fact, when you look at cases of large-scale atrocities, you find that very few men and women recognized the situations as gravely concerning. Most people simply accepted them as the status quo.

A chill spread through me as I thought of all the people, my own relatives included, who looked the other way as crimes against humanity occurred in their countries, and even in their immediate communities. I know from the letters and diaries I've seen that these folks in my family tree were "good people" by anyone's standard. They loved God, their families, and did what they could to make the world a better place. If they could have let one of the greatest tragedies of human history play out all around them, and yet not recognize it as tragedy, what on earth makes me think that I'd have the clarity that they lacked? The odds are, I wouldn't.

So how would you know? Since it's so terrifyingly easy to go with the flow of whatever your culture says is okay, to let a sense of normalcy override any gut feelings that tell you there's a problem, how could you get the perspective to see it? What does it take to figure out that you and your family are on track to be the people in the faded photographs that future generations will look at and say, "How could they have let it happen?"

There is one litmus test that works every time.

The great atrocities of human history are varied and their details, as well as in the amount and type of human suffering involved. But there is one thing that every single one of them has in common: In each case, the victims were categorized as something less than human. Whether we're talking about slavery or infanticide or genocide, the only way that large groups of otherwise nice folks let it happen is because they'd come to believe that the the people being harmed were not really "people," in the traditional sense of the word. Good people don't put up with evil. Normal, upstanding citizens would never allow human beings to be killed or enslaved right under their noses. The only way that evil ever works is through word games, i.e. through lies.

Take a moment, look around, and ask, "Is there a term widely used in my society that is specifically designed to strip away the human dignity of a specific group of people?" This is a litmus test that would flush out hidden atrocities in every case. The Tutsi in Rwanda, the Jews and other ethnic minorities in World War, the newborns of pagan Rome, the African Americans in the early United States -- each one of these groups had labels applied to them that implied that they were subhuman.

So what happens if we apply this litmus test to our own age? Does such a label exist, one that should tip off all people of good will to the fact that something terrible is happening all around them?

I think that the answer is yes, and that that term is fetus.