Bonhoeffer discusses the danger of allowing the judgment of an individual or society to determine who has the right to live, and draws a conclusion that applies both to abortion and to euthanasia. The distinction between life that is worth living and life that is not worth living must sooner or later destroy life itself. To kill the innocent would be, in the extreme sense, arbitrary. In this entire discussion Bonhoeffer was careful to draw a distinction between innocent and guilty persons. The distinction is crucial.
Arbitrary killing is the taking of innocent life.
There is nothing arbitrary, he asserts, in the killing of criminals, nor in killing the enemy in time of war. It is, nonetheless, of crucial importance in the ethical questions of daily life. Dietrich Bonhoeffer, op.eit.