> the police were willing to use purchasing habits/items as circumstantial evidence to go after the wrong person.

Hopefully it is not a great leap in logic to see that the justice system was what went wrong, not the club card thing.

The problem is that you assume your thoughts on justice worldwide.

China may have a totally different understanding on what is allowed and what not. The whole privacy data thing doesn't worry me very much in my country. But it's scary when i think of other countries.

The best way to put it is that large quantities of data by themselves are not evil and can do no harm. It's how people use them that matters. Once these large data stores are created it is impossible to anticipate all of the bad ways that people will use the data. It's disingenuous to claim that just because the data has never been used in a certain way that it never will be used in that way in the future.

It's the same as claiming that your privacy is safe because the company has a 'privacy policy' in place. In reality, the privacy policy say that it can change at any time and that the company has no legal obligation to notify you of these changes. These policies may change due to a change in direction at the company, or because the company is losing money and decides to sell that information to the highest bidder to stay afloat... Maybe the company is even swallowed by a larger company that then revokes all of the old privacy policies...

On the cynical side, the system cannot be fixed, so it is better to avoid the 'club card thing' so as not to give ammunition to those who would wield it against you.