The Washington Post has an interesting article in its archives: "What will future generations condemn us for?" The author, Kwame Anthony Appiah, notes that throughout history, societies have had moral blind spots:
Looking back at such horrors [such as slavery and lynching], 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?
Appiah offers a list of characteristics of past blind spots to help us spot our present ones:
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.
These are interesting observations, and they seem to be true, but I think Appiah misses the key element of these past atrocities: they involved a denial of intrinsic human value in a particular group of human beings.
Why is it that Prohibition inspired so much fervor, only to die out, while our horror at slavery continues to grow? The answer is that unlike Prohibition, slavery was a crime against the dignity of a group of human beings. This is the factor that, oddly enough, explains both our current condemnation of slavery and its former acceptance. Because for some reason, crimes against human dignity seem to be at the same time the most atrocious offenses of a society (as recognized by future generations) and the offenses most difficult for the people of the time to spot.
Perhaps this is because people have much to gain from exploiting and/or disposing of others, but in order to do so, our intuition of intrinsic human value must be actively suppressed. (Or it could be our intuition extends only to people who look like us, and universal value must be either learned or reasoned to from knowledge of our own value.) Once a society convinces itself that one particular group of human beings is not as valuable as everyone else, not fully human for whatever reason, its conscience is freed to seek the gain it desires, so it has a powerful drive to justify itself. And unfortunately, as in the case of slavery, once the arguments separating one group of people from the rest of valuable humanity are commonly accepted, it's very difficult for anyone to see past them.
So if we are trying to discover our blind spots, it seems to me we should be most suspicious of our culture ignoring arguments that human dignity is being violated in some way, particularly if listening to those arguments would inconvenience us.
By now you probably have a major moral blind spot in mind for our culture. See if it ends up in the list Appiah compiles using his criteria:
1. Our prison system
2. Industrial meat production
3. The institutionalized and isolated elderly
4. The environment