Even a fist can be lethal, either by design or bad luck.
When you start using weapons, you start risking deaths.
That's not to say that all use of weapons is always morally, wrong, but it IS designed to deflate the idea that force can be used without risk.
A few years back Boston cops use a "non lethal" pepper ball, shot a student straight in the eye, penetrated her brain, and dropped her in a fraction of a second, stone dead.
http://www.boston.com/sports/baseball/redsox/articles/2004/1...
Police also kill people all the time using "non lethal" tasers. The firm manufacturing them and the police have a vested and shared interest in denying that any of these deaths were actually caused by the weapons; it is - apparently - sheerest coincidence that people die of heart attacks at the same time that they're hit with 50,000 volts.