And you think that a father being gone from his life for years had nothing to do with his mental problems?
I can tell you from my own interactions with young men and women is that the kind of numbness described in Mr. Lanza is often caused by personal trauma. Is it not possible that his father walking out of the home contributed to this kind of mental trauma?
To the level of schizophrenia and worse is usually a biochemical problem unless severe abuse was involved. Absence of proper parenting can lead to some functional problems, however, severe mental problems are physical and chemical.