Self defence is not a reason to have a gun either. If guns were outlawed altogether then no one would have them. ( a little naive I know) I know you can say criminals will just use some other weapon such as a knife or whatever, but it is easier to defend against a knife than a gun. Ever tried to outrun a bullet?
The problem is that 'people would still have them. Thinking that outlawing guns will result in no guns in the hands of criminals is similar to saying that because exotic reptiles are banned from private ownership people do not have them. Same goes for illegal drugs. I seriously doubt criminals would buy weapons from legal sources anyway. I do get your point though, unfortunately people with not so-good intentions will always have access to 'guns'.
(Just my opinion)
-Will