And yet, the press keeps on reporting these "reliable intelligence-based" reports of impending attacks on the "homeland" as though you should believe them.
Salted with the FBI's warnings are triumphant announcements of terrorists who were interrupted mid-plot, who inevitably turn out to be some mix of not-actually-terrorists or gormless-nuts-without-a-hope who've been entrapped by FBI provocateurs. The most recent example is the "50 ISIS arrests" leading up to July 4.
Actual attacks — the Times Square Bomber, the underwear bomber, the shoe bomber, the Boston Marathon bombers — occurred with no warning.
The problem is three fold:
The FBI has all the incentive in the world to issue warnings and no incentive whatsoever to not issue warnings. Issuing warnings has no downside, while not doing so is all downside.
The FBI, like all agencies of the government, does not operate in a political vacuum. Emphasizing the "ISIS threat" at home necessarily helps prop up the broader war effort the FBI's boss, the president of the United States, must sell to a war-weary public. The incentive is to therefore highlight the smallest threats. This was a feature that did not go unnoticed during the Bush years, but has since fallen out of fashion.
It has no actual utility. What does it mean to be "more vigilant"? It's a vague call to alertness that officials, aside from "beefing up security" by local police, never quite explain what it means. If the FBI wanted to tell local police departments to up their security of the 4th of July weekend, surely they could do so quietly, without the chair of the House Committee on Homeland Security having to go on all major networks talking over b-roll of ISIS in apocalyptic terms.
(via Wil Wheaton)