Just putting my 2 cents in.
I do not think that citizens have a need to be running around with firearms, in fact some countries don't even give out guns to the police that lightly and they still remain efficient.
If you say you need a gun to defend, against what? A trespasser breaking in to your house? Most of the times you'll have more than enough time to call the police and have them deal with it. Yes there is always the possibility you will have to confront him to defend your family, but in this case, if there's no guns, the most you'll have is a knife? a baseball bat? and what will he have? the same weapons that are available to you. Yet knives have a far more practical use such as used cooking. What purpose to guns serve? As well, if someone walks in to a school with a knife in an intent to kill people, he'd be far less successful than walking in with something that is DESIGNED to take many lives with just a press of a button.
Organised terrorist are a whole other matter, they most likely can get their hands on guns regardless of the law, and if you need up being a target of such group, I doubt a gun would help you much.