No, I don't know all the workings of Juan Williams's brain and all the factors that contributed to his making such a fear connection. But since he has no doubt had many peaceful, even friendly, encounters with people wearing "Muslim garb" and since the 9-11 hijackers were not so attired, it's hard to imagine that working for Fox "News" and being surrounded by the anti-Muslim sentiments that are so often expressed by some of their talking heads wasn't a major factor. The 9-11 hijackers also had dark complexions and were male, but Williams' gut level fear is apparently aroused more by an old woman wearing a hijab than by a young dark-skinned man wearing jeans and a t-shirt.

You're right, mg, the brain does make very quick associations. And propaganda contributes a lot to such associations being made.