They are generally not, which leads some people to think that classifying guns as "tools" would let guns fall under the non-regulation scheme that otherwise applies to tools. That's why I said that the point was arguable.
However, the issue of guns is mainly emotional. The antigunners' appeals are emotional. If we're going to fight that, we have to bring in emotions on the pro-gun side. Calling guns "tools" takes away that emotional connection. In fact, to gun owners, guns are much more than tools. That's why, on balance, calling guns "tools" makes them easier to regulate. It concedes the emotional ground to the antigunners.
The antigunners surely know that guns are not just "tools." Actually, the strongest argument on the pro-gun side is that guns are symbolic of freedom, both on a personal and societal level. This has nothing to do with their utility as tools.
The issue with guns is mainly legal, with respect to regulation and gun control. Emotions have a play in this for manipulative purposes, but in the end it's the legal aspect which counts.
People will always be emotional about things, some more so than others. But their emotional response has nothing to do with whether or not things are tools.
If calling guns "tools" takes away the emotional connection, and antigunner's appeals are emotional, then calling them "tools" cannot make them easier to regulate. The whole push behind gun control laws is emotional...that's how the left pushes it.
Guns are tools. They're self-defense tools, sporting tools, hunting tools, and yes...tools for illicit acts such as theft, burglary, rape, and murder. They are tools for oppression and tools for freedom.
And, if you watch enough old westerns, you'll probably see where they're also tools for nailing up wanted posters.
Computers are tools, saws are tools, pens are tools, needles are tools, even rocks and sticks are tools. Tools are devices used to carry out some function.
What that tool may be might be defined by design, by use, or both. A curtain, for example, is a tool used to shade windows and block view through windows. Yank it down and use it in the garage to wipe up oil, and now it's a rag.
Guns are only different in what they can do. But they're still tools which accomplish nothing unless someone wields it as such.