The job is only dangerous in the big cities.
You have some weird conceptions about big cities. Homicide rates aren't an urban vs. rural thing, they're a north vs. south thing . It's the south that has the high per-capita murder rate. Which is in turn because said areas are the poorest places in the US. The trend holds true even in areas that are relatively culturally homogenous - for example, there's not much of a difference in culture between northwest Texas rural counties and northeast Texas rural counties, but northwest Texas is much wealthier per-capita, and also has a much lower homicide rate.
The TL/DR: crime correlates with despair, and places like the Mississippi Delta are characterized by chronic high unemployment, low wages, and limited access to quality education and resources. This combines with a legacy of racial violence/mistrust and lax firearm laws, and the result is exactly what one would expect.
One could make the argument that, well, okay, it may be the rural south that has a high murder rate per capita, okay, but there's lots of people in big cities, so it's a multiplier. Yes, that's true, but there's also lots of cops in big cities, so it doesn't change their odds of being the one responding to a situation where shots are fired, to the degree that police departments are equally well staffed per-capita.
It's also worth mentioning that the rural crime rate trends in the US are much worse than the urban crime rate trends. I hate to risk derailing this by the meremention of Trump, but he tapped into a very legitimate wellspring of anger; the economic growth in the US over the past several decades has been very uneven, and a lot of people, esp. in rural areas, the rust belt, and the south have felt left behind, with insufficient care from politicians as to their plight. While the ragebait media landscape has tended to try to focus their anger on cities and minorities, as "evil outsiders catered to by elites", US cities are, frankly, doing quite well on average, and have thrived in the US's growing service economy. But people in the rural south, the Mississippi Delta, the rust belt, etc (outside of the "energy belts", like in west Texas, that produce oil, gas, wind power, etc)... their lived experiences of a lack of opportunity and declining communities are very much real. They're just projecting them (wrongly) onto big cities outside of their region.