Recently, a review of the FBI found that it left about 24,000 people on their terror watch list improperly--AND left off those who actually posed a threat. After 9/11 their watch list grew to an astounding 1 million of various people American and not. If there is one very dangerous thing for a government that wants to be democratic to do, it's to start imagining that its own citizens are enemies.
It has happened, to ill effect, in the past and will happen again in the US. We seem to have an extremely short memory, at least when someone seems to threaten us from the outside. But, I think the real danger in the US, and maybe elsewhere, is in over zealous fear of each other fanned by a media that seems to repeat every word the Executive branch gives them. It took an election to provide a corrective.