I find myself in the "whatever I'm prepared to use to cause harm to someone is a weapon," and “whatever I'm not prepared to use to cause harm to someone isn't a weapon" camp.
While there is some merit in the concept of not hiding behind semantics so that our firearms can be made to seem, to those who want to take them, less threatening, using the word “weapon” to describe every firearm is semantically flawed and harmful to the cause of protecting RKBA.
Webster defines a weapon as “1: something (as a club, knife or gun) used to injure, defeat, or destroy 2: a means of contending against another.” That second definition is key, as it includes the concept of using something to coerce another person. Coercive use of a thing also makes that thing a weapon.
How can one say that a baseball bat or a knife can be a weapon but is not always a weapon, then say that a firearm is always a weapon? If how a thing is employed determines its "weaponness," then that principle must be universal. Webster agrees—it puts guns into the same category as knives and clubs, saying that how they are used is what makes them weapons.
I don't buy the notion that guns are always weapons because they were invented to produce harm against other people. They were actually invented purely for the amusement of those who invented them. Their potential for use as weapons was very quickly discovered, of course. But they were invented as curiosities.
But if a gun is not a weapon until it is employed to injure, defeat, destroy, or coerce--what is it? Is it the same as a baseball bat or a knife? Not exactly.
Imagine a linear scale on which we could place anything; I'll call it the Human Coercion and Lethality Potential (HCLP) scale. One end of the HCLP scale is near zero; things there have very little to no potential to be coercive or lethal to a person and/or could be coercive or lethal only under a very narrow range of conditions. At the other end are those things that have extremely high potential to be coercive or lethal to a human under a wide range of conditions.
Near Zero _________________________ Moderate _________________________ High _________Extremely High
What things could we place on Near Zero end of the HCLP scale? A crayon, maybe? How about a shoestring? Both have limited coercive/lethality potential, and only under very specific conditions. In the normal course of life they are not considered weapons. A bat and even a knife fall short of the high range of the spectrum because their use as a weapon requires close contact with the subject (granted, a knife can be thrown, but then it's a projectile). A firearm has very high potential because it can be employed in a lethal manner from a distance under an almost unlimited set of conditions and has a great measure of coercive power. (Extremely high would be reserved for WMD, well beyond our current scope.)
Firearms are among the few instruments accessible to the average person that can achieve a condition of very high human coercive and lethality potential. Every functional gun in our safes can be brought into this condition; loading a gun and aiming it at another person creates this condition straight away. That fact alone sets guns apart from clubs and knives, and it is by and large the reason why anti-gun people are anti gun and not anti-club/knife. But in and of itself it does not make all firearms "weapons." Many of us own firearms that we did not acquire for any sort of defensive or coercive purpose. These are not weapons.
Going back to original premise, intended use universally determines a thing’s "weaponness." Nothing is a weapon until one employs it in such an intentional manner as to give that person the ability to cause harm to or coerce another person. M16s carried by soldiers are weapons because the reason they are carrying them is so they have the ability to inflict harm on or coerce other people. When I carry a sidearm (incidentally, my permit is a CHP, Concealed Handgun Permit; the word "weapon" doesn't appear on it anywhere), that firearm is a weapon because having the ability to prevent harm to myself by causing harm to or coercing another person is the reason why I'm carrying it.
A gun that's not meant by its owner to give him the ability to injure, defeat, destroy, or coerce other people should the need arise is not a weapon. It is an implement, much as a screwdriver, a violin, or a car. It is a person's mindset that makes something a weapon, nothing more.