Another thing I like about Arpaly's book is her careful disambiguation of eight senses of 'autonomy':
(1) Agent-autonomy: self-control, or acting on your explicit 'best judgment' (in contrast to akrasia).
(2) Personal efficacy or the ability to take care of yourself (in contrast to domestic 'dependents').
(3) Independence of mind: in contrast to blind 'followers' and brainwashing victims.
(4) Normative, moral autonomy: what's violated when one is hit or stolen from.
(5) Authenticity: being true to yourself, or acting on what are in fact your deep concerns.
(6) Self-identification: feeling unconflicted, and acting on what you perceive as your deep concerns. (This differs from authenticity since one's self-image could be inaccurate.)
(7) 'Heroic' autonomy: supposedly possessed only by ubermensch. (I'm a little unclear on this one.)
(8) Reasons responsiveness: the ability to recognize and respond to reasons.
Arpaly suggests that only the last of these is strictly necessary for moral responsibility. (It's also true that someone incapable of agent-autonomy won't be a moral agent, but she suggests that this is because both have the same precondition: being a reflective creature.) In any case, Arpaly seems right in observing that mere lapses in agent-autonomy don't excuse: there are plenty of blameworthy akratic actions (and some praiseworthy ones too, cf. Huck Finn).
A couple more notes:
* Authenticity is also relevant to (the degree of) moral responsibility, insofar as we are more praiseworthy or blameworthy, on her account, when the morally significant concerns behind our actions are deeper concerns of ours.
* Historicism about responsibility (the view that whether S is morally responsible in phi-ing depends on extrinsic historical facts about how S came to be the way she is) may partly be motivated by confusing 'independence of mind' [which is an uncontroversially historical notion] with other -- more important -- ahistorical senses of 'autonomy'.
* In light of all this ambiguity, we might do better to retire the word 'autonomy' in favour of whichever precise sense we have in mind: self-control, mental independence, authenticity, reasons-responsiveness, or whatever.