Its actually quite simple. If I'm a robber and I know that you are armed, I'm going to think twice about breaking into your house because I know that you are armed and that you could kill me. I know that certain States in the USA allow you to carry a gun in public. I think indiana and Texas allow you to actually carry guns in public. Guess what the crime rate goes down. If you are a criminal, wouldn't you rather shoot someone that is unarmed, then take a chance of getting killed by someone that is armed. Since criminals obtain most or all of their weapons illegally and don't register their fire arms, they wouldn't turn them in. On the other hand, law abiding citizens would be force to give up their firearms since they are registered, and they would be completely disarmed. Banning guns would also make street gangs, criminals, and thugs really happy because now they get the green light to do what ever they want. They can break in, kill you and your family and by the time you call the cops, your whole family is dead.