Starting with the first post office shooting in 1986 and following the growing trend, "Murder by Proxy" examines the factors which first provoked such an extreme degree of workplace violence. You have to know something untoward was going on when survivors of a shooting (A) can't immediately guess who the shooter is because they say any one of them could have been driven to it, (B) sympathize to varying degrees with the shooter, and (C) deface the name of one of the victims on the memorial, the tyrannical supervisor they deemed responsible. The larger societal issue at fault seems to be the dehumanization of the workplace in general, and the establishment of an environment which more readily creates disaffected and alienated individuals who feel victimized and oppressed.
The term "murder by proxy" was coined to describe the expression of violence against innocent individuals. "You can't murder the post office," they say, so the next best thing is to murder the post office's workforce. The problem has only escalated now that these original incidents have provided a paradigm for other disaffected and alienated individuals who now shoot up malls, theaters, schools, or any other soft target available. Unfortunately, the mass shooting is now too much a part of the American experience to just go away, and this hackneyed attempt to prevent these tragedies with more gun control is too imbecilic for words.
If you have time, feel free to watch the whole thing. Just ignore the annoying narrator; he's quiet most of the time.