In Bonhoeffer's Letters and Papers from Prison we find a succinct and compelling expression of this in a paper-fragment titled 'Who Stands His Ground?' The following excerpt quotes roughly half of that paper:
'The great masquerade of evil has wrought havoc with all our ethical preconceptions. This appearance of evil in the guise of light, beneficence and historical necessity is utterly bewildering to anyone nurtured in our traditional ethical systems. But for the Christian who frames his life on the Bible it simply confirms the radical evilness of evil.
[Before continuing, Bonhoeffer considers and finds wanting the 'ethical systems' of 'rationalism', 'moral fanaticism', reliance on one's 'conscience', and 'duty'.]
What then of the man of freedom? He is the man who aspires to stand his ground in the world, who values the necessary deed more highly than a clear conscience or the duties of his calling, who is ready to sacrifice a barren principle for a fruitful compromise or a barren mediocrity for a fruitful radicalism. What then of him? He must beware lest his freedom should become his own undoing. For in choosing the lesser of two evils he may fail to see that the greater evil he seeks to avoid may prove the lesser. Here we have the raw material of tragedy.
Some seek refuge from the rough-and-tumble of public life in the sanctuary of their own private virtue. Such men however are compelled to seal their lips and shut their eyes to the injustice around them. Only at the cost of self-deception can they keep themselves pure from the defilements incurred by responsible action. For all that they achieve, that which they leave undone will still torment their peace of mind. They will either go to pieces in face of disquiet, or develop into the most hypocritical of all Pharisees.
Who stands his ground? Only the man whose ultimate criterion is not his reason, his principles, his conscience, his freedom or his virtue, but who is ready to sacrifice all these things when he is called to obedient and responsible action in faith and exclusive allegiance to God. The responsible man seeks to make his whole life a response to the question and call of God.'
- quoted from pages 135-7 of the 1960 Fontana publication
(bold print added, masculine language refers to all persons)
I'm sure there are plenty of others who are far ahead of me in their thinking on this, but I offer it here because--to quote Sheriff Ed Tom Bell from No Country for Old Men--'it has left quite an impression on me'. In fact, one might quote that character even further in responding to Bonhoeffer:
'I always knew you had to be willing to die to even do this job. But, I don't want to push my chips forward and go out and meet something I don't understand. A man would have to put his soul at hazard. He'd have to say, "O.K., I'll be part of this world."'