Unless you're a professional shooter, such as in the Olympics? Some people make a living using a gun that never kills anything. Even police rarely fire their weapons. They are more often used to foster compliance without any injury than to kill.
But yes, in general killing or potential killing is the purpose. But this reasoning implies that killing is bad even when there are legitimate circumstances.
I think your reasoning is flawed. When you are aiming for targets with a gun, there is no utility in that. That's like saying a basketball is a tool. Neither guns nor basketballs are tools.
Also, I never once implied that killing is bad. For example, killing animals for food is not bad. Also, killing someone who is trying to kill you is not bad.
"something (such as an instrument or apparatus) used in performing an operation or necessary in the practice of a vocation or profession"
Websters even considers books as tools as they relate to scholars. By the definition, they are tools. In the context of hunting (and policing, and self defense), they absolutely offer utility.
I don't know what you meant to imply or not. But colloquially, when those statements are made they usually imply a negative view of it. I would bet that more than a few readers would have read it with that in mind. What is evident based on your prior comment and this one is that you do not consider utility to include killing.
> general killing or potential killing is the purpose
I'd like to emphasize the "potential" here even more - one of the greatest uses of guns is as as a deterrent, and this is worth differentiating from actually killing.
People who claim that the only use for a gun is to kill are factually wrong, and you can point this out.
But yes, in general killing or potential killing is the purpose. But this reasoning implies that killing is bad even when there are legitimate circumstances.