If you are a philosopher like Aristotle or maybe a legislator in the business of judging the actions of lesser mortals, you need a template, a measure, by which to rule and hand out honors and punishments.
To do this you probably need to be able to "distinguish between the voluntary and the involuntary" action. Sometimes, of course, you have to do something, such as throw goods overboard in a storm, that you would normally never do voluntarily. And sometimes you would face death rather than voluntarily do something evil.
But what about things done by reason of ignorance? Obviously, says Aristotle, everything "done by reason of ignorance is not voluntary". Now he makes a fine distinction. Suppose you do something in ignorance that you would presumably not do voluntarily. If you repent of your action, your action is "involuntary." If you do not repent, your action is "not voluntary."
So, says Aristotle, if you throw a pointed spear at a friend, thinking that your spear "had a button on it", your action would be involuntary, since you would surely repent of your action. That is action in ignorance that is involuntary. It is hard to think of an action in ignorance that is "not voluntary," i.e., not repented. Suppose you threw a pointed spear at an enemy thinking it had a button on it. Would you regret the action when the poor chap fell down dead? If you didn't regret, the action in ignorance would be "not voluntary." Perhaps a better example would be Candidate Romney saying that he doesn't worry about the "very poor." Everyone thinks that this is a stunning error, because conservatives do too worry about the poor. But if the struggling middle--the folks that Romney says he does worry about--were to wake up and say to themselves, "Wow, finally a politician that cares about us and not the bloody poor!" then Romney would not repent of the action in ignorance. So that would be action in ignorance that is "not voluntary."
But Aristotle is not yet done. He does not want to admit that actions due to anger or appetite could be involuntary. The "wicked man is ignorant of what he ought to do" but that does not make his ignorance involuntary. Actions done in ignorance but where "the moving principle is in the agent himself" are voluntary. Thus we could say that the liberal welfare state policies that have cratered the working class are voluntary. Liberals may have been ignorant of the specific consequences of their policies, but they cannot hide from the results. It is evil to encourage people to exchange their birthright for a mess of pottage. Period.