It's disingenuous to suggest that the solution is simply keeping them off the internet. Their own proprietary network cables/radio comms can be spliced into and

It's disingenuous to suggest that the solution is simply keeping them off the internet. Their own proprietary network cables/radio comms can be spliced into and reverse engineered when running through public places. Low-level employees can be tricked into plugging in flash drives (i.e. Stuxnet). When you're building a target, security aneeds to be designed for across the board. If you want to shortcut your way out of that, don't use general-purpose operating systems and don't build networks.