Unfortunately, there is no way to protect against all the craziness in the world. If I'm not mistaken, there was a man in China that went off and slashed 37 people, I believe. Then there are those that feel that blowing up people, and often themselves, is the way to support their particular religious or political beliefs. Frankly, sometimes it only takes some skilled oratory to aid in causing the deaths of millions such as was the case with Adolf Hitler and the National Socialists.
In the United States we have a constitutionally guaranteed right to bear arms. Does that mean that everybody should arm themselves? No. But there are cases where just the fact that a citizen may be legally armed has lessened the violent crime rate because criminals usually prefer not to risk ending up on the receiving end of violence they initiate.
In the recent incident in Oregon, a legally armed citizen may have saved lives by being prepared to engage the shooter. Although he didn't take a shot because his training caused him to realize he didn't have a clear shot. But his actions might have resulted in the assailant retreating to a stairwell where he took his own life. While it would have been better if the perpetrator had not shot anyone, how many more lives were saved by the armed citizens actions.
I believe the UK has, for the most part, disarmed its population. At least, in terms of firearms. Now you can hardly sell a kitchen knife online because knives have become the weapon most readily available to most hoodlums over there. I suppose almost anything can be used as a weapon with a little ingenuity. Frankly, I've seen people that the only thing they need is a set of car keys to become a lethal threat.
While the shooting at the school is a tragedy, let us not use it as an excuse to try to take away our rights to our access to a means of defense of ourselves and our loved ones should the need arise. If some wacko with a gun comes trying to shoot my wife or grandkids, they pretty much had best take me out first.