I have.
I have met some seriously screwed up people who had a Secret, at least.
Remember a complete whackjob like Robert Hanssen was doing counterintel on the Soviets for the FBI. It would be awfullly hard to surprise me.
It's certainly possible for good guys to go bad, but it's usually due to an obvious motivation like pure greed, which was the case for Hanssen. What would this guy's motive be?
And Ivins wasn't some weird loner, he had a long-time wife and children. I still say that something stinks here.