The "grave damage to national security" wasn't something an official said. It was a warning inside the document.
Certainly there are instances where this is the case. I can think of a few others to add to your example.
But there's no good reason to assume that all invocations of classified and politically or strategically sensitive material are excuses to cover up incompetence, negligence or breaches of law. And in fact in this case I'm not sure what it would be covering up. What's listed here is hardly incompetence nor negligence and the argument for breach of law, while slightly stronger, wouldn't pass a smell test.
Certainly there are instances where this is the case. I can think of a few others to add to your example.
But there's no good reason to assume that all invocations of classified and politically or strategically sensitive material are excuses to cover up incompetence, negligence or breaches of law. And in fact in this case I'm not sure what it would be covering up. What's listed here is hardly incompetence nor negligence and the argument for breach of law, while slightly stronger, wouldn't pass a smell test.