BBC news if often behind the times in terms of Asian affairs, as stated on the BBC news article, such events have happened, several times, in China in recent years, due to public ignorance/negligence of the importance of mental health in Chinese society.
As this question is posted under Yahoo! UK, I assume that's where you're from, then you would know carrying a knife in public is seen as dangerous in British society. As guns are illegal, knife crime dominates British society as compared to gun crime dominating American society.
Guns are more dangerous than knives, which is their designed purpose, to legalise civilian gun possession will only escalate crimes, not reducing them.
Police forces exist as a reason - British police officers do not carry guns, instead use stun-guns if they have to, and consequently a smaller death rate in crime-related violence in comparison to the US.
America seem to be peculiar in that it is the only developed country that allows civilian gun possession, any relevance to America having the highest crime rates amongst developed countries?