Well, people dissuading a killer/murderer by brandishing a gun and people being otherwise killed by guns are both very rare events, so I'd say that if one is "just fear-mongering" so is the other. In practice it's very hard to figure out whether gun ownership causes a reduction in crime, because it's well known that crime causes gun ownership and you have to have to be lucky in finding a good natural experiment to get around that. I'm not aware of any convincing research on the subject one way or the other, I'm afraid.
And before bringing up the number of gun deaths that would be considered justified versus suicides or murders, we do have pretty good evidence that in those cases where a gun prevents a crime it's mostly by the threat of its use, not its use itself.
And before bringing up the number of gun deaths that would be considered justified versus suicides or murders, we do have pretty good evidence that in those cases where a gun prevents a crime it's mostly by the threat of its use, not its use itself.