What part of the IRA used legally owned firearms? That guy on the right is carrying an AG-3, stoled from a Norwegian army depot. According to VG, a Norwegian newspaper, it took a junior high school student less than an hour to buy a loaded pistol on the streets of Oslo. Even if you destroyed every gun on the planet, it would only require a half-decent workshop to make one.
http://www.amazon.com/The-Do---Yourself-Submachine-Gun/dp/0873648404/
Ok now I have made my diy submachine gun! Now lets go to the shops to get some ammo, what?? ammunition is banned as well as guns here?? 'searches amazon for diy 9mm ammo manual' machine lathe please! oh no theres no gunpowder for sale?? Lets get some potassium nitrate...what its banned? 'It is over here btw' I have to use a Sten gun mag? Oh wait they don't sell them here, ok look for make sten gun mag on amazon.
You see your argument here is absolutely ridiculous, its like someone owning a business thinking of putting a fence up to protect it, "oh but someone could just climb over it, cut through it" Doors?? "Oh but someone could smash it in" why bother?
Its like a bank reasoning that the money should not be in a safe because if someone tried really hard they could break into it.
I am pretty sure the idea is a deterrant and to make it as difficult as possible for someone to do, we know that if someone is absolutely determined with anything they will go ahead but the percentage of people going to those lengths or having the means and knowhow to do so will always be smaller even with nutjobs, simply because it is a lot harder to do.
You will only ever be lowering the odds with this approach but I will bet the chances of it happening are infinitely smaller than if he could walk into a store and buy a gun and ammo legally.