It makes more sense to me to remove the violently insane from society than to try to remove all inanimate objects from society. He could have gotten a job in a restaurant and stolen a cleaver and some butcher knives. He could have built a big bomb with fertilizer and kerosene or household cleaning products. He could have taken a car or truck and run down dozens when they were gathered outside for a rally. Where does the danger really lie in the object or the person? This ain't rocket science. If common sense makes no headway in your debate I think it's safe to conclude that the people you're talking to have chosen to ignore reason.
Wait...you said he had been deemed a danger to himself and others but Belasarius in #16 said the opposite.
And if he was not allowed to buy a gun how did he get one?
You see, their point is the system did not work.
Remember..I am playing devils advocate here.