A new normative theory and a PhD thesis Bitter Crank: First let me say thank you for reading my work and providing your thoughts. The issue about freedom over one's own mind is something I would like to discuss in my thesis objections chapter. Would you mind if I referenced you as someone who had brought up this objection? If you wouldn't mind, please message me your name so I can reference you properly as I fear calling my detractors bitter cranks won't go over well in my thesis :).
That said, let me try to deal with these issues in order.
First, I think I have made it reasonably clear that I am talking about morality in an objective, universal sense, and not just referring to a system of cultural norms. So it isn't really an issue that Hitler thought he was acting rightly, because he wasn't.
Second, it seems to go over okay so far, but if I only said things my supervisors agreed with, I wouldn't be much of a philosopher.
As for the main issue here, I am not convinced that when someone blurts something unkind and uncharacteristic out unthinkingly, that they are in any sense not acting freely. I am inclined to agree that we do not choose to like or dislike things (though it seems we can choose to attempt to cultivate a like or dislike in ourselves which may or may not be successful), but I think we are free to choose our actions. When we say "felt the uncontrollable urge to punch someone in the face", I would say we are being poetic, rather than precisely describing what is happening in our minds. Firstly, we are still the ones acting, there is no one and nothing else making the choice but us. Secondly, I would say that we can choose how to act in these situations and when we choose to act in a way which is wrong, we are morally culpable for them. The fact that you are very angry doesn't make you hit someone, you still choose to, although the choice may be made quickly and influenced by the person's emotional state. To put it another way, a person does not need to be good at controlling their temper in order to be free.
But, supposing that people exist for whom turning around and slugging someone in the face really isn't a choice, but is rather an automatic action, like a reflex. I would suggest we might want to hold them at least partially morally responsible for this conduct after they know that they have this kind of reflex, if they do not take reasonable steps to avoid situations where they might violently assault another person without intending to. Much in the same way as we might want to hold Cyclops responsible for destroying a building because his glasses got knocked slightly, because he went out with two cannons attached to his face and only a pair of sunnies preventing them from going off... or some other example that doesn't involve one of the X-Men.
As for how free a person needs to be, I would say that the question is ill-formed. A being either has free will, or they don't. That is, they either have the ability to make choices that are not wholly determined by preceding or external factors, or they don't. If we had several more reflexes, we wouldn't be "less free", though there may be fewer things over which we have freedom. If we imagine an alien that has a mass of tentacles that all act independently of its intentions, to ward of predators, absorb nutrients, etc, and could only control its head, then it could still have just as much free will as any other person. So I would say that having free will or not is a dichotomy and not a sliding scale.