I'd say the difference is that a gun doesn't HAVE any other use-case. Its purpose is exclusively to injure or kill living things.
Also, there's definitely a difference in the capabilities of each tool. The severity of what a gun is capable if is a heck of a lot higher than what an LLM agent is capable of (doomsdayers notwithstanding).
I do generally agree with you, though. America's gun violence problem is not reeeeally a function of America having more guns. That's just an exacerbating factor.