Critical Question: Are there rival causes?

Each of the following examples provides an argument to support a causal claim. Try to generate rival causes for such claims. Then try to determine how much you have weakened the author's claim by knowledge of rival causes.

Passage 2

Why did the postal worker go berserk and kill those six employees? The answer is provided by a close look at his childhood. He lost his mother when he was 8, and his father often physically abused him. Also, he grew up in the shadow of more successful older siblings. As a child he had a difficult time making friends and had trouble establishing a sexual identity. Then, as an adult he drifted from job to job, while developing increasingly bizarre fantasies. Eventually, the post office became a symbol of the society that had caused his failures. To become "somebody," he ultimately turned to violence.