Why? Because such measures could "reinforce prejudices and stigmatise the affected social groups in the perception of the public." Horror of horrors! Better to have another jihad terror attack in Europe than...the perception of Islamophobia!
From Reuters, with thanks to Romy:
BERLIN (Reuters) - A Moroccan man won a landmark legal victory on Tuesday when Germany's highest court set strict limits on the ability of police to trawl electronic databases at random in search of possible terrorists.
The Constitutional Court said such data trawling, for example to identify foreign male Muslim students, was only lawful if there was a concrete threat to Germany or one of its regions, or a danger to human life or freedom.
"A general threat situation, of the kind that has existed continuously in regard to terrorist attacks since September 11, 2001, or external political tensions, are not sufficient," the court said.
"The pre-condition is, rather, the existence of further facts pointing to a concrete danger, such as the preparation or commission of terrorist attacks."
The case arose from a complaint brought by a Moroccan student after the September 11 attacks on the United States, when German police began scanning local authority and university databases to identify Muslim men aged 18 to 40 who were current or former students.
Men who met that description were then subjected to further police checks in an attempt to uncover more al Qaeda "sleepers" like the three Hamburg-based Arab students who led the suicide hijack attacks on America. None were actually found....
The German court ruling said general police trawling of electronic records exposed the people concerned to an increased risk of further investigation.
It added that if such measures became publicly known, they could "reinforce prejudices and stigmatise the affected social groups in the perception of the public".