Suppose you are a student and someone in school says he's going to shoot it up. They're probably just making it up and you would be a traitor if you ratted on them. Remember, for every person who is prepared to fire his father's weapon, there are thousands who would not do it. Besides, most schools now have security, so it isn't your role to get another student in trouble. This is not only about school.
People also carry guns in the workplace to get attention.
Usually a semiautomatic will do the job. The truth of the matter is that, for every gun in America, there is someone capable of firing it. I'm not advocating this, but the gun is so much a part of our culture, you're a fool to think it's going away. I know I have. I can't keep track anymore.