That's a common miss-belief. Its false on so many levels, but people keep believing in it even after it has been found to be false every single time it has been said.

To take an example with wiretaps in US. First they said that any data found about innocent bystanders would be imminently destroyed. A few years later, they change the rules to keep it, but proclaimed that it was just 60 days. Years later, they put out a small press release and changed it to 5 months.

Or take the Swedish wiretap law. Politians and collumnist promised high and low that it would never, EVER, be used for anything but terrorism threats outside the national border. They said that anyone believing otherwise was tinfoil hats, and just misunderstood the issue. Before a year had passed, the secret police (for internal security) was granted an exception. A few months later, government politicians got an exception. At the same time, the police got an exception to target serious crime. A few months further down, and it was talks about using the data for our version of IRS.

Yes, never ever indeed.