Even though I'm largely against air gaps as a defensive measure, there is something to this. Though I think the breadth of the problem isn't properly appreciated. It's too dimensional. There are too many unforeseen interactions and complications with computers and the humans in the organizations that run them. Even leaving aside moles[0] people trust to easily and often have interests that are odds with their organization.

[0] Which, why should we? The world has moles.