Earlier quoted context omitted.
They can't control their weapons because they have to operate in a society that can't control its weapons...
Other countries have plenty of weapons around, yet don't have police that use deadly force immediately. Finland is a prime example[1]. [1] https://en.wikipedia.org/wiki/Estimated_number_of_guns_per_c...
Finland has a national murder rate of 1.6. [1] At first that doesn't seem too bad as our murder rate is "only" about 300% higher. But that comparison by itself is quite misleading. Crime, and especially the most violent crimes including murder, are not evenly distributed in the US. They're heavily centralized into relatively small areas. So for instance these [2] are the crime data for Ferguson, Missouri where Michael Brown was killed. In the year Michael Brown was killed, their homicide rate was double the US average. It's now skyrocketed to 42.8 - 2,675% higher than Finland.
To give some context to that 42.8 the murder rate in Mexico is 16.35. In Columbia it's 26.5. As a matter of fact, in terms of nations - there are only 5 places in the world more dangerous than Ferguson, Missouri -- a town of some 20k people. I'm certainly not condoning police actions, but at the same time I think people don't really consider these situations in terms of context. Somebody, seemingly without irony, suggested we ought disarm the police. Imagine disarmed police in Mexico.. now increase the danger they face by 300%. That's what disarming police in areas like Ferguson, Missouri would be akin to.
This sort of reality is very foreign to us, who I suspect for the most part have led very privileged lives. And so we extrapolate our lives to a situation where suddenly the police are just killing people. And that would indeed be insane. It's so foreign for us to imagine how dangerous many places in the US are -- and it's these locations where the systemic police violence tends to also be heavily centralized.
[1] - https://en.wikipedia.org/wiki/List_of_countries_by_intention...
[2] - http://www.city-data.com/crime/crime-Ferguson-Missouri.html