I'm not a cop, nor have I ever been, so take this for what it's worth...
The risk of being shot isn't that high, but it happens (happened to a friend of mine recently). You're more likely to die in a wreck than be killed by a BG. Being a farmer or a miner is more dangerous to you physically.
However, the mental toll is unlike any other job in the world. You see the worst kind of people in the worst kind of circumstances on a daily basis. Nobody calls the police to report their neighbors are being nice to them, or that their husband came home early from work and brought flowers; they call because the SHTF, and they need help. Other than that, people don't want to deal with you (think about it). Cops have extraordinarily high divorce rates, alcoholism, suicide, etc, etc. And there are real reasons for that. Imagine how hard it would be to trust people if every day at work everyone lied to you ("I really thought I was doing 60" to "no, I have no idea who beat up my wife" to "I'm working on getting you a raise") and a big part of your job was cleaning up the messes (car wrecks, homicides, suicides, domestic abuse, etc.) that no one else wants to know about, much less see?
If that's a job you want, go for it. I respect the people who do it every day and keep themselves together, but it's not for me.