Thousands of items can be used as a weapon. If you put aside home-made bombs, a gun is all too often a nasty weapon in public. Many can outrun a baseball bat, knife etc.. and the thug using such a weapon might find quite a few people are ready to tackle him/her to beat the crap out of them. With a gun, distance and the severity of the injury are totally different. So the answer that's claimed to work is, more guns. And as America demonstrates, more guns = more incidents = more deaths. Doesn't matter if you own a gun, if someone shoots you before you know anything, you're dead. They don't stand there and shout, "Cooey, I have a gun/machete/knife/brick and I'm giving you advance warning that I'm going to attack you".
These school/work place etc.. shooting attackers are cowards, they're scum and it spoils it for everyone else. But if you do what you've always done, you will get what you've always got. Nothing will come of this latest mass killing of kids, and I wonder how many more times this year there will be a thread on another incident like this.