Your analogy doesn't really work because you can't copy a gun. These tools are way more dangerous than a gun because you can replicate them very quickly. You can never destroy the tools once they are created, someone always has a copy.
This is what scares me more than nuclear weapons. A nuke requires a huge amount of people and infrastructure to maintain and launch. But a digital weapon? Pfft, copy that shit onto a USB key and one guy can wipe out power stations across the entire country.
Because you left an infected usb key or ten in the power station parking lot, the power of human curiosity, and the marginal cost of proactively protecting against something "very unlikely" by e.g. epoxying usb slots because procedure says it can't happen.
Your incredulity would be fully justified in the 1990s, but with every year that passes, it is becoming harder and harder to fully isolate computer systems from other computer systems. I'd like to think I wouldn't let untrusted devices near my power plant, but I have some sympathy for those who struggle to keep their stuff secure in a world where security is ever harder to achieve.
This is what scares me more than nuclear weapons. A nuke requires a huge amount of people and infrastructure to maintain and launch. But a digital weapon? Pfft, copy that shit onto a USB key and one guy can wipe out power stations across the entire country.