Your assuming competence. The surveillance state is built by the lowest bidder and is far far less useful than generally assumed.
Just look into false positives on the no fly list. Sure, it's slightly better than random chance, but odds are if you pick an name from that list they are a non threat. (It's far worse than that you can probably pick several names before finding a real issue.)
Depends on how you define accuracy. Your thinking in terms of the test for the no fly list is X accurate, but that does not mean the no fly list it's self has X accuracy. List A, contains every person on the planet so it's comprehensive, but nobody would call that an accurate no fly list. List B contains one name of an terrorist who has made specific credible and recent threats, it is very accurate.
I think what's really being alluded to is that regardless of your accuracy (unless it's 0% or 100%), your false-positives will always be subject to your inputs.
Put another way, if you have no terrorists going through, then your false positive matches will always be greater than or equal to your positive matches, and in this case, equal only when they are both zero, since there would never be a real positive.
In a less extreme case, such as the reality we live in, we have many millions of non-terrorists and a few terrorists, and even with three nines of accuracy, it's likely your false positive matches far outweigh your real positive matches.
Just look into false positives on the no fly list. Sure, it's slightly better than random chance, but odds are if you pick an name from that list they are a non threat. (It's far worse than that you can probably pick several names before finding a real issue.)