Reader David R. wins for first response. It’s from the 1930 play “The Decision” and the line in question comes from the “Control Chorus”:

Who fights for Communism must be able to fight and not to fight, to say the truth and not to say the truth, to render and to deny a service, to keep a promise and to break a promise, to go into danger and to avoid danger, to be known and to be unknown. Who fights for Communism has of all the virtues only one: that he fights for Communism.

The play was widely seen as an apology for totalitarianism — which would be the obvious conclusion I would think. It seems his family banned its performance until 1998.