If you tell the public everything, you risk panic and further depression of an already depressed economy. Disagreements on economic theory aside, I think most will agree that the level of "confidence" amongst the People has a profound impact on the functioning of the economy. So, there is the incentive to remain silent, or at least ambiguous.
Ambigious is the worst way to be. So you scare people, but tell them not to worry.
So you destroy trust.
I didnt' say they had to say everything - there is a need to *keep* some security assets, sometimes. But if they're going to come out and say "everybody look out, tomorrow's going to be an attack, but we won't tell you where or when, and oh, go about your daily routine" - that's stupid.
We need to change the daily routine, obviously. Pretending otherwise - *And* presuming the government will save us from everything is a mistake.
Addison