It's the argument that proponents of gun regulation would make.
Second of all, there is some additional risk to others by you being armed, even if it's never stolen. Could be very small...but there is some. Some kid might find it and shoot himself or you might use it mistakenly against someone or someone might accidentally be shoot. Of course, there is also a benefit to others by you being armed, as the more people are armed, the less likely criminals are to commit crimes against others, even unarmed people. There's also a benefit to yourself by being armed, in that you have a greater degree of self defense. I guess my point is that all of that risk and benefit needs to be weighed out.
You're right that the use of cars poses a greater risk to people than the ownership of a gun. But that's my point...with cars, the risk is balanced by the use of cars being highly regulated. You have to be licensed to use one and even then, there are lots of traffic laws governing how you use it and a dedicated portion of police to monitor people's use of them. Not saying that's how it ought to be, but that's how it is.
I think "reasonable" proponents of gun regulation see guns like they see cars, a dangerous but useful tool that needs some regulation to offset the risks.
I also think pro-gun people who resist ANY effort to license or regulate the use of guns should also resist ANY efforts to license or regulate the use of cars, to be consistent.
Personally, I have no idea how much regulation is the perfect amount for either cars or guns...but would lean towards a minimal amount for both. That's why I favor a bunch of states having a bunch of policies, so we can actually SEE what works by experimentation.