[bellaire]

Very real and legitimate objections based on a right to privacy aside, the main flaw with this point of view is this: "If there's almost 0 chance..."

Almost 0 is not zero. If you're monitoring 300 million people, and the chance of a false positive is, say 0.001% per person per day, that's still 3,000 false positives every day. The false positive signal far outweighs the signal from the "real" dangerous people, making the system pointless and useless. Even if it works 100% of the time on the intended targets, human operators will become too fatigued from dealing with the false positives to deal with them effectively.