Ar. use of the story of Alcmaeon is an interesting one. In the story, Alcmaeon's father Amphiaraus compells Alcmaeon to kill his mother, who had been manipulating his father, or else be cursed by his father's. Under such constraints, Alcmaeon chooses to kill his own mother. The point of this story, for Ar., is that we cannot always easily accept other's claims that they had no other choice. Ar. does not consider Alcmaeon's actions to be counter-voluntary, despite the enormous strains of the situation. Personally, I struggled with this point as well, given the extreme nature of the situation that Alcmaeon was faced with. Broadie and Rowe's commentary on the subject, made Ar. thinking more clear to me. They write that 1) his actions were clearly voluntary as their origin was in him and 2) that Alcmaeon's actions were so inexcusable because even when one is faced with two unbearable alternatives, it is ultimately less blameworthy to be forced to experience one of the alternatives than to voluntarily choose one(pp. 312). But while this explanation is informative, I think it could still be argued that when stuck between two unbearable alternatives, it can sometimes be wiser to choose the evil that you know, rather than be entirely at the mercy of the circumstances. For instance, the curse that Alcmaeon murdered his mother in fear of could be far more disastrous than we know. But I digress. I only wish to point out that this example is a rather complex and potentially confusing one.