Why is the murder rate in the US so high?

The alienation Americans feel from each other, the lack of meaningful human connection, makes it easier to stifle empathy and end another's life. For all America's material wealth, its technical sophistication, it has failed to improve on the things humans need most. Psychiatric pharmacology cannot replace familial emotional connections or a sense of community. Convenience and assembly line processes cannot replace meaningful work that one can take pride in. American life becomes a competition for wealth, encouraging people to regard one another as enemies. The people, their needs perpetually unmet, forget exactly what it is they are lacking, and are puzzled and frustrated when their children are unsatisfied. Each generation becomes successively more disconnected from their own humanity. Violence in media is the result of this, a symptom, not a cause.

There are many reasons for murder in every culture. Americans simply more often lack the reasons to refrain from it: empathy, any shred of hope that their life could improve, having a worthwhile life they wouldn't want to lose due to incarceration or execution, etc.

Jam it back in, in the dark.