Since the Dutch secret service put up camera's at Amsterdam Central Station there have been no suicide bombings or other terrorist attacks. That proves the method works! Right? Not really.
There has never been a suicide bombing or terrorist attack at Amsterdam Central Station. Or anywhere in The Netherlands for that matter. Ever.
Claiming camera's prevent those attacks and illegaly listening in on citizen's phonecalls helps against terror so it's all worth the loss of privacy and billions of euro's is the same as claiming the number of children dropping has to do with the declining number of storks. Proving storks deliver babies. Or putting a banana in your ear helps keep alligators away from Sesame Street. Just try to disprove that fact!