Well, you know the line, it’s the motto devised by the NRA, the famous peace and love club.
First  time I heard it I admit I was taken aback and couldn’t help thinking,  well, sounds true in the end. And yet, I knew there was a hitch but  where was it hidden?
Let's see how it works in other situations.
-  It’s not the saw that cuts the branch of the tree it’s the one who uses  the saw. Huh? And if he has no saw? Well he’ll use an axe. But if he  has no tool can he cut the branch? Humm… obviously not, he needs some  kind of device but he alone can’t do anything. There’s interdependency  between both a tool and someone to use it.
Not really convincing still.
- Let’s try with something else:
It’s not the plane which flies, it’s the pilot who makes it fly.
Hummm… I feel there’s some kind of trick here.
- Sugar doesn’t cause diabetes, it’s the one who eats sugar. 
- Tobacco doesn’t cause cancer, it’s the one who smokes.
And on and on and on…
It’s very confusing really because at first glance you can’t dismiss the apparent logic of the line.  
Now, let’s have a look at Aristotle and his notorious
 4 causes.
Isn’t  it clearer now that when someone came with the line we’re discussing he  actually constructed a sentence with 2 final causes included?
The  gun is the final cause because it has been designed and manufactured in  order to kill and nothing else. It’s a tool like any other one.
Man is the efficient cause because without him there would be neither guns nor any other tools.
Each  tool has been conceived with one specific goal, the ultimate goal of  the gun being to kill whereas the man wasn’t born to kill (well, for  some happy-triggers you may wonder indeed).
Here lies  the trick then: To artificially put on the same level the man and the  tool (here the gun) he fabricated, e.g. to hop over the efficient cause  in order to have 2 final causes in the same sentence, which is logically  impossible since it comes down to circular thinking. A = B then B = A.  Well, great... and where do we go with that?
Plutôt que de recourir à la logique classique, essayons autre chose : la réfutation par l'absurde (ad absurdum)
The  NRA mantra is basically a trivial tautology. Of course, without men,  tools are ineffective (be it a saw, a hammer or a submarine). Well, this  is sheer common sense and pure tautology. 
If guns  didn't kill people, criminals could resort on the sole lethal power of  their frightful look. But it's inefficient so they use the tool most  effective to accomplish their wishes. 
Some try by  throwing balls made of paper but it doesn't really work. And yet they do  try hard... It's not the will only that kills people, it's the tool,  e.g. the guns which raison d'être is to kill. 
If guns  don't kill people then I'm happy to learn that Abe Lincoln didn't die  because a bullet smashed his head off. And the same goes for Kennedy.  Bullets didn't cause their death I'm told, just the will of the  murderers.
Ca tient de la transmission de pensée là...
Since  we're at it, how many Americans are shot before they can react and kill  the would-be killers? I have a feeling there are more innocent victims  than the other way round like we've seen again no later than last year in Fort Hood. Of all places where all victims were suposed to be armed!
- If guns don't kill people, people do, why  didn't William Calley, convicted as a war criminal by the US judiciary,  end his life behind the bars? 
As I wrote above, will doesn't suffice to kill, a tool is necessary, be it a chainsaw, a gun or an iron bar. 
If not, then P. Tibbets is 
personally responsible for the death of 80.000 Japanese, not the atom bomb. 
The guys who turned the taps open are 
personally responsible for the death of 6 million Jews, not Zyklon B. 
The American pilots who dropped million tons of napalm in Vietnam are 
personally  responsible for the death of, say, one million Vietnamese, not the  bombs. Unless it was R. McNamara who wasn't even in the planes over  Vietnam.
There has been an earthquake last January in  Haiti. If we admit the logics of the NRA line, whose will is behind the  250.000 dead in Haiti? The tectonic plates (as weapons) or... God  himself who created all things on earth? 
En fait ce  slogan de la NRA n'a d'autre raison d'être que de donner bonne  conscience et déresponsabiliser les clients des armureries du pays. Il  faut faire marcher le commerce et une bonne accroche marketing  logiquement trompeuse légitime moralement ce commerce.