I think "the authorities" track record leads to a lot of this.
The only terror attack we've received so far (9/11) was correctly identified as such pretty quickly. In contrast, the now inane "Nothing to see folks, move along" sarcastic post has been made 1,000 times on FR, and each times indeed it ended up being nothing. Yet no matter how many times these paranoid cynics' ignorant prognastications prove to be wrong, they still return each time to insist that if she floats, she must be a witch.