As a psychologist of virtue development, I find abhorrent behavior a puzzle. Did the person enjoy doing what he did or did he feel like he could not help himself?
If he enjoyed hurting others, then it was a vicious act (vice). Vice is the result of learning to enjoy the wrong things. "Wrong" things are those actions or activities that lead to less well-being in you and/or your community.
If the person felt like he could not help the action, that he did not wish to act this way but the passion or ideas of the moment carried him along, then it was an incontinent act (underdeveloped character). An incontinent person wants to be virtuous but has conflicting emotions and desires to which he succumbs. He is not strong enough to resist the incompatible desires.
Another person might feel like hurting someone, but is strong enough to resist the desire, having other more powerful desires. This person is not virtuous either, but merely continent. This person has to continue to work at shaping his desires and habits in such a way that they become harmonious with his good judgment. When he no longer feels like harming others and feels like doing (and does) the right thing (and there is no desire to do anything vicious), he becomes virtuous.
But of course it is much easier to become virtuous if you start life with a virtue-encouraging environment (e.g., virtuous models, virtuous practice, lots of love and support). Working on virtue later in life can be an uphill battle with long-practiced vices hard to eradicate.
We live in a society where we are almost forcibly encouraged to develop vice, to develop habits that are not good for our well being. Here are some examples. We are constantly encouraged to eat harmful food products which are formulated to become addicting (Kessler, 2009), leading to obesity and other health problems. We learn to love to shop endlessly for things we don't need, consuming the earth's resources (story of stuff, other report I sent). Several researchers have demonstrated that consumerism leads to less well-being all around (Kasser, 2003).
We live in a toxic sea of violent television, movies and games which change our mind about what normal human behavior is like and desensitize us to victims (Strasburger, Wilson & Jordan, 2008). Most of my students think humans are naturally violent and selfish. But if they had grown up before radio, television and movies, chances are their everyday experience of people would have led them to believe that humans are naturally cooperative and altruistic. In the current context of violent media saturation, when we see real-life human violence we are likely to accept it as "humans being humans," rather than viewing it as a symptom of human pain, injustice, or needs unmet.
So I would argue that vice and vicious character have become more prevalent in our society due to our recklessly poor understanding of human needs. We have boiled human needs down to materialistic assets: job, home, car, food. But the most important aspect of a good life is social support (Cacioppo & Patrick, 2009), which our social practices keep shredding. We concurrently immerse our children and youth in a toxic environment (Gabarino, 1999) and provide far less guidance to them than they need. The village that used to raise the children (extended family especially) has moved away.
Aristotle implied that individuals have one character--vicious, incontinent, continent or virtuous. But we know in behavioral science that character is not of one piece. You have different skills and dispositions in different realms of life. You can be virtuous in one area or with one person (e.g., with your child), continent in another (e.g., with your mother-in-law), incontinent in another (e.g., eating junk food), and vicious in another (with that neighbor who has opposing political views).
But back to Major Nidal Malik Hasan. Was Hasan vicious or incontinent? He did not have much social support. He was a loner who did not have the skills to get along with others except in superficial ways. If it takes a village to raise a virtuous person, then the village failed in his case.
Does it matter to our analysis if he was an ideologue who believed that America and its military are evil? This brings us back to truthiness, the feeling that something is true so it must be true, regardless of the facts. Ideology is a type of truthiness.
Truthy ideology can come from incontinence---there is some desire for truth but we get off the rail when we glom onto an attractive idea without thinking carefully. You can dream your way into evil.
Or, truthy ideology can come from viciousness---a refusal to think carefully or compassionately about "the enemy." We see this in Osama bin Laden. And perhaps in Hasan.
Truthy ideology kills, whether from incontinence or viciousness.