Shortly before I was born, the town where I grew up was attacked by terrorists of a certain religious/ethnic group. Only five people were killed, more by good luck than anything else. Fifty more were injured as they drank. The country was horrified, and demanded revenge.

Immediately after the attack, and another similar one, the government passed a law allowing it to counter the Evil Certain Religious/Ethnic Group Terrorist Menace by detaining suspected terrorists without the normal legal safeguards.

The police made good use of the new law: only three days after it was signed, they arrested four young people from the relevant religious/ethnic group and persuaded them to confess to everything. A year later, the four were convicted of murder.

15 years later, a different court accepted that the police had beaten them into confessing, and that they lied in court to secure a conviction. The four were acquited. Civilised people across the country and the world hoped that this would be the last time the desire for revenge against the Evil Certain Religious/Ethnic Group Terrorist Menace drove the country to lose its senses.

Of course, nobody ever learns anything.