German Interior Minister Thomas de Maziere is excited. For him, the pilot project at Berlin's Südkreuz train station constitutes an "incredible security victory."

Were de Maiziere to see his role more as a guardian of fundamental rights, rather than as minister of the interior, he'd be less likely to say this and more likely to acknowledge that German Bar Association president Ulrich Schellenberg is correct when he writes that "we are moving toward a surveillance state that gives us less and less space."

Systems provided by three different manufacturers have been undergoing tests at the Südkreuz station since the beginning of August. Three hundred volunteers are taking part in the test program, which will determine which cameras are best at recognizing participants as they walk past. The goal is that an alarm would sound as soon as a specific face - that of a potential terror suspect, for instance - is picked up by the cameras.

Read more:  Opinion: Facial recognition security technology needs to be tested

Ineffective, but all-encompassing

A similar test was started back in 2007. That trial, at Mainz's main station, failed because the technology was still too inefficient. Things have changed in a decade: In some post office branches and supermarkets, customers' faces are analyzed so that they can be shown personalized advertisements. And social networks such as Facebook and search engines like Google are making facial recognition part of our daily lives.

Yet the current trial, at a busy station in the capital, has a different quality about it. You can avoid shops that use such technology. You can be careful with how you share your own data on social media. But should people really have to avoid going to places because there are cameras present? That would turn vast swaths of German city centers and almost the entire public transport network into no-go areas for privacy-minded people.

Read more:  Germany's facial recognition pilot program divides public

One fatal flaw of facial recognition tests in city centers is that they don't deliver what they promise; another is that they encroach on people's privacy far more than many think. The technology is ineffective because none of the most recent terror attacks would have been prevented by it. But still it's all-encompassing because current laws on German ID cards mean that security services can directly call up images of everybody's biometric photograph from passport authorities. As a result anybody with a German passport can be identified - responsible citizens are turned into potential suspects.

Public space has been of particular importance to democracies ever since the Ancient Agora of Athens. It's the place for social meetings, for public displays and for the resolution of conflict. It's where the individual meets the population at large. Article 8 of Germany's Basic Law acknowledges this by guaranteeing freedom of assembly. A dangerous imbalance emerges by allowing state authorities to check people's locations and patterns of movement at any time using cameras and facial recognition.

Can we guarantee that such a system will only be used to search for terrorists or serious criminals? Or will it not at some point be used to track down tax evaders or small-time drug dealers or - further down the line - to root out adulterers or politically undesirable people?

The public space is currently being threatened from two sides: by terrorists using bombs or, increasingly, vehicles or knives, and by the would-be omnipotent security services that pay no heed to our right to privacy. On the bright side, you can engage in a political dialogue with the latter group. We should take advantage of this opportunity.