"on launch" is for specific ICBM systems we know have nuclear warheads in them and monitor by satelite. That is not what would be used here. Automated systems cannot tell the difference between a bomber carrying a nuke and one carrying a conventional warhead. They cannot tell the difference between a normal ballistic missile and one carrying a small nuke. Until it goes off and people notice. There is no automated counter launch for that scenario as we would not even know its a nuke until it goes off. And if it already went off we clearly know where it was going. Iran, Ukraine, Russia, and the US launch missles at eachother constantly. All they need to do is stick a nuke in one of them.