I've had security clearances for several decades. In my first job in government, a summer long ago, while still awaiting my clearance to come through, I wrote a paper which my boss deemed worth sending to several other offices and embassies -- and which he promptly classified "Confidential," thereby denying me the right to read it until my clearance eventually was granted.
I've had access to Top Secret materials, atomic energy information, and even intelligence community products. While I've seen some questionable classification actions, I've also learned the value of keeping classified information secret from those without the need or right to know.
When I read Daniel Ellsberg's fascinating -- and of course self-serving -- autobiography a few years ago, I was struck by one passage in which he recounts a conversation with Henry Kissinger at the start of the Nixon administration. Kevin Drum repeats that passage today. I think it tells powerful truth: that many officials become too enamored of classified information and too willing to trust it more than contradictory open source information. I think the priesthood of secrecy is too closed for wise policymaking.