My only gripe with what you said is that there are legitimately irresponsible drivers and irresponsible gun owners. I don’t think there’s anything you can say to most Americans who own a gun to get them to not. Guns are so tied to the American image, it’s not a tool, or a hobby…it’s a fetish, a symbol of belonging to the group.

The car argument isn’t a bad one, but saying that everyone is responsible until they’re not is a falsehood.

A better way to phrase it might be something along the lines of:
Even responsible drivers can make an error, and a single error, one split second of inattentiveness, can destroy the lives of so many people. Now consider how many people are irresponsible drivers.