The WWII years in Germany are much like plague years. Those who went through them won't talk much of them, and those who came after don't focus on them much. A distant cousin talked of it “As awakening from a terrible nightmare, and not wanting to remember what it was”.
Bonhoffer, and others like him, serve as powerfull witnesses to those who survived. If you ask a typical German WWII survivor about Hitler they will say “He seemed so good for a time!” and he did. But they will also admit, that even when he stopped seeming good, that they didn't want to stop believing in him. For the consequences of that meant something would have to be done.
Now the regular soldiers often recognized this first, which is why on the Eastern front there were numerous plots to kill Hitler and stage a coup. But for civilians, the illusion lasted longer even in the towns outside the death camps. Bonhoeffer not only saw past that illusion, he worked against it. First by shuttling Jews out of the country, and then by the bomb attempt. To Germans of that era, and even today, it is a very powerful witness that not all were fooled, and perhaps they should not have been either.
People don't like to be confronted in that way, and will be very upset at the one who destroys the illusion. Hence, Bonhoeffer and others who were involved are not looked as heroes, but as fools and villains.
Very good post. I reread “The Cost of Discipleship” ever few years and EVERY time I come away with a deeper appreciation of the absolute necessity to try to do God’s Will regardless of the consequences.