That doesn't really make sense. Dehumanization is the result of severe trauma, not just a disconnect from society. Just LIVING IN RURAL AREA doesn't make people more likely to dehumanize/be dehumanized. Not just anything can trigger a complete disconnect from reality (ie a psychotic break) in anyone, it happens specifically to those who are mentally ill, and with the most common psychotic breaks resulting from schizophrenia (iirc) the symptoms should develop a few days/weeks prior to the break and it should be able to be prevented.
The REAL ones you have to worry about are people afflicted with anti-social personality disorder, which is just the fancy word for psychopath or sociopath (although these people are usually older). They can seem like perfectly normal, and even appealing people, but one day they could just burst in shooting, and no one would expect it.
No you would have had to read more carefully, so maybe that's my fault. Let me make this clearer. Those in a rural area are more apt to commit suicide. Just take a look at suicide rates across the United States.
Let me make the connection between psychological isolation and dehumanization. Rarely, people choose to be isolated without some social mores influencing them in some way. To be outcasted is going to create an isolation, because those who do not follow the social norms are thrown into "prison" by the "norm police" It's also going to create an uncomfortable feeling in the isolated individual, a feeling that they're less than human (or at least the people who do not accept the individual into their culture, subculture or whatever). That individual's feeling can foster into a personality disorder such as anti-social personality disorder, if you like the DSM-IV, you'll know that roughly 75% of all inmates have been diagnosed with this. Basically, they're not in prison because they have a mental disorder, they have been labelled with ASPD because they're in prison, a characteristic of the disorder is that they've been in trouble with the law. Also it is important to remember that it can happen to anyone. You're not born with a personality disorder, and it's not exclusive to certain individuals, could be males, females, white, black, poor, rich.
There are a lot of things that can cause someone to break. One of those things is when people hold onto their resentment. That's what causes drug addicts to use, and it certainly cause one to partake in other destructive behavior. If school shootings were easy to predict, and prevent, there would never be one. The fact is, they're not as predictable as we think they are. Just because you can point out tell tale signs in postidiction, doesn't mean you can find them before the incident occurred.
Think about it, the likelihood of this happening is slim, and you cant blame someone for a shooting before they do it. You can only TRY to get them help, but many times they're feelings are under the radar, and there's not much you can do to stop something like this from happening.