4. Records might be data-mined for "patterns of suspicious activity" to detect criminals. This might produce false positives.
It will produce false positives. Say you have a database of 60 millon people, 100,000 of which are criminals. If the system is 99% accurate it will correctly identify 99,000 criminals and accuse 600,000 innocent people of being criminals.
Generally speaking, if the ratio of law abiding citizens to criminals is r, then r innocent people will be wrongly accused for every criminal the system misses, regardless how accurate the system is. To reduce the false results it can only become more and more intrusive, making us all jailbirds.
Five is a sufficiently close approximation to infinity. -- Robert Firth "One, two, five." -- Monty Python and the Holy Grail