Since the purpose of an object can change rapidly and be hidden easily (example: IEDs), any rules based on the intent of an object are highly impractical. Outlaw guns, and only outlaws will use guns 
people will just use knives, bombs, poison...
people will just use knives, bombs, poison...Why did you strike this sentence through?
« Outlaw guns, and only outlaws will use guns. »
This is just plain truth. By outlawing guns, the State makes peaceful people defenseless against violent people. It is just silly.
True, but it's one of those "big bad anti-gun control memes" Because pithy truisms are bad, you know.
Why would nations who have nukes decrease their number then? Even on mutual agreement?
Because maintenance is pretty expensive.
Exactly! Now let's transfer this back to people and gun-space: I just don't want to maintain a gun! So let's agree on a mutual agreement, that we don't own guns.I'll pass, I find gun maintenance to not only be inexpensive, but also a great "moment of zen". Now, I agree, having to maintain hundreds or thousands of guns would probably be a little arduous. So, tell you what, let's each limit our gun ownership to 50, OK?