Knabe is noted for several works on oppression in the former Communist states of Eastern Europe, particularly in East Germany.

Knabe was active in the peace movement, and he founded in 1978 a committee in support of Rudolf Bahro, a German philosopher imprisoned in East Germany.

He said: "Not until the Communist dictatorship is as firmly in mind in Germany as the criminal regime of the Nazis will we really have succeeded in coming to terms with the legacy of Stasi minister Erich Mielke.

With the avowed intent to call the East German regime to account, Knabe supports pro-business and anti-socialist views.

In a blog post, he criticized the red–red–green coalition of the Berlin state government for what he described as kowtowing to the extremism of The Left party, which he alleged to be riddled with former SED and Stasi personnel intent on bringing back the old regime to the city-state.