Voting for social welfare nets is the extent of their "goodness." That's all they have to do to prove to the world (and themselves) that they "care." They don't want to take any longer dealing with their own morality than it takes to pull that "D" lever.
Fear, and avoidance and denial to themselves.
Have you ever read any books by Oliver Sacks? He's a neurologist who has chronicled the most interesting case studies of brain injuries in the US. (He wrote "Awakenings"--Robin Williams played him in the movie) What I found particularly interesting is that a certain number of his patients were sometimes particularly exasperating to deal with because the nature of their brain injuries left them completely unaware that they were injured. While they are obviously physiological causes of denial, it was interesting to see the way their minds worked.
If you do choose to read him, I recommend "The Man Who Mistook his Wife for a Hat" to start. Each chapter is a different patient, each one fascinating in his own way. You should be able to find them in the science section of your library.
And yes, Rats are completely unaware that they [are] injured.
Your analogy with brain injuries is apt. I haven't read Sacks, though his books look familiar. At one point, I spent some time with such brain and mind studies. I tended more toward the conceptual -- Sacks appears to be more anecdotal in his presentation than I would have preferred.
Good stuff, however you choose to come at it.