Why are there so many jerks in the Army? There are at least two theories.
One says that the Army, and the nature of being a Soldier, attracts mean people. Knowing that military life can involve extreme violence, disruptions in personal and family life, and a lifestyle of deprivation, the meaner elements of society volunteer.
Another holds that the Army takes otherwise decent people and makes them mean. The rank structure, a culture that stifles and demeans, and an organization that frustrates natural human tendencies of freedom and creativity will ultimately drive niceness out of a person.
A third plausible explanation is based on my small sample size. I am deployed with the 40th ID from Southern California, and many would argue that SoCal has more than its share of jerks, so they are highly-represented on this deployment.
The third option is intriguing, but doesn't explain all the mean people I've met along the way or the many mean transplants to Southern California. No, either of the two main theories seems to offer a better explanation.