If the misery of our poor be caused not by the laws of nature, but by our institutions, great is our sin.
-- Charles Darwin, Voyage of the Beagle
One cannot help but be somewhat frightened by a family cursed with schizophrenia or manic-depression or family violence. But the mind is very good at building barriers to keep frightening thoughts at bay. The barriers go up so quickly that one is usually neither frightened nor empathic for long. Similarly, it is hard to avoid feeling a little bit superior to a family suffering problems created by low intelligence or drug addiction or alcoholism. Seeing a family afflicted by any of these various genetic liabilities, one of the first barriers to go up is the conviction that this can't possibly happen to my family. We're too healthy or too lucky, too smart or too good, for something like this to happen. One can easily develop a certain cynicism; this terrible problem is affecting them, so they must in some way deserve it. Either they did something awful, or they foolishly exposed themselves to risk, or they are simply not as nice as they seem. But this kind of thinking is only a defense against the truly frightening realization that anything can happen to anyone, and that no one is truly safe.
Some families choose to bear children, despite having been afflicted generation after generation by a genetic liability, only to see their children suffer problems as well. One's first sympathetic response to a family like this may be attenuated by the feeling that these people should never have had children. Aren't they aware of the problem that has held them back all their life? Don't they care that their children may be similarly affected?