I don't know if I'd make a blanket statement like that. I'm pretty sure hand grenades should be banned since they are essentially useless for hunting, self-defense, etc.
Yes, I'm aware that you didn't say a grenade was a gun, but the implication is that all weapons should be legal, right?
I think when most people say that its usually within an idea of reason. Nobody says that you should be able to carry a rocket launcher into a school.
I personally think that weapons shouldn't be allowed in the school in the hands of delinquents and have them only accessible to experienced adults. Adults that have been screened for sanity and responsible use. I think an armed teacher or a school guard is a great idea.
I also think the age at which you can buy a weapon for the exception of a handgun to be increased dramatically. Specifically on rifles and shotguns. 21 for a handgun here is fine. But i find it kind of irking that a 16 year old can legally own a shotgun or a large rifle in my state. I don't trust kids to be right in the head.