Any weapon analogy is bad for our side of the argument, because weapons sound to many people like things that bad people use to do bad things. Yes, I realize that knives are used in kitchens to cut vegetables, but with the way this discussion is rightly framed as a security thing, people are not thinking about kitchens.
I would prefer to see lock analogies. Here's a half baked example: This is like a law requiring all builders of buildings to install locks that can be opened by any person who gets access to a copy of a law enforcement key.
Personally I like that analogy because it was recently revealed that people can 3D print working keys from a photo of a key. So even the "physical" key is vulnerable to security attacks of a digital nature. All someone needs to do is get a photo of the global "key" and they can then get into anybody's safe.
No more difficult to produce than many illicit drugs. Potentially much easier even, with the right parts. Besides, there are plenty of other countries you can smuggle arms into the U.S. from given sufficient demand.
Of course the knife analogy is still useful. We all know the futility of outlawing software.
This is more akin to knife control.