Benghazi is not the capital of Libya. Tripoli is. Had Stevens stayed there, he'd have been safe. But he decided to pay a visit to the U.S. Special Mission in Benghazi, where there was an active uprising.
He was, I'm sure, aware he wasn't entirely safe. As is our ambassador in Kyiv. And I'm quite sure no one who works with our foreign service people has forgotten about what happened in Benghazi.