But I agree, I doubt we have the stomach for it... But if we really were under serious attack from a specific country we could and should do it.
What are being hacked...public info sites that we could all
go to if we wanted? That would not be so worrisome. If the government is providing public password doorways so that some bureuacrat can access secret data(not normally available to the public) from his laptop at home then that is worrisome.
Secret data nets should not be connected in any way to public nets no matter if firewalled or not and should only be accessible by going into the main offices and accessing dedicated systems or by direct hard wire/fiber systems not wired in to any public systems.
NK uses servers based in Japan so not that easy to cut them off.