[Significantly updated and moved-to-front from Feb 7.]
Suppose Adam wrongly - i.e. without sufficient reason - kills Bob. Though there's no real justification for killing Bob, such an action may nonetheless be excused if it was done unwittingly, at least if the agent's ignorance was itself non-culpable. But what if Adam was previously negligent -- i.e. his ignorance culpable* -- does this mean he's blameworthy for the action after all (at least to some degree)? I think the literature on this topic has been plagued by some serious conceptual confusions. Let me explain.
Holly Smith, in her seminal (1983) paper 'Culpable Ignorance' [pdf], considers cases in which an earlier, "benighting act" foreseeably causes our agent to later be deprived of evidence that would have led him to refrain from committing the bad "unwitting act". In one example, the agent impermissibly leaves behind his driving glasses, and so unwittingly runs over a pedestrian that he otherwise would have seen. (As will become clear, I think these are deviant cases of 'culpability' in ignorance, but more on that later.)
As HS points out, all can agree that Adam is blameworthy for the benighting act. (This is meant to be built into the specification of the case.) Further, there's a clear sense in which this makes him responsible for the ultimate outcome: "the unwitting act is a risked upshot of the benighting act", and we're responsible, roughly speaking, for the foreseeable risks that eventuate from our reckless actions (compare Russian roulette). HS thus diagnoses the debate over whether culpable ignorance is exculpating as just an instance of the moral luck debate, i.e. whether agents become more blameworthy if the foreseeable risks of their reckless or negligent acts actually eventuate.
This seems a misdiagnosis.** Let's distinguish two ways in which Adam - already culpable for the benighting act - might come to be doubly blameworthy due to the occurrence of the unwitting act. It could be that the eventuating harms render him more blameworthy in his earlier act of negligence. That's 'moral luck'. Or it could be that he is now blameworthy on more occasions: not just in the benighting act, but in the unwitting act (qua act) as well. That would be 'culpable ignorance'* failing to excuse the unwitting act as a second occasion of blameworthy agency.
Note that one might think that (even culpable*) ignorance excuses the unwitting act, in the sense that we cannot blame Adam qua agent of the unwitting act, whilst nevertheless blaming him (qua agent of the benighting act) more because of this bad outcome. So the question whether culpable ignorance excuses the unwitting act is orthogonal to the 'moral luck' issue of whether the unwitting outcome makes the (earlier) agent more blameworthy.
[N.B. If you're suspicious of this talk of "earlier" and "later" agents, you can easily translate it into talk of how the later event makes the enduring agent more blameworthy "in" acting as they did earlier. That is, I'm not really making any metaphysical claims about persistence through time here. I'm just using such talk as a convenient shorthand for locating the agent's responsibility. We may speak of that exercise of agency in virtue of which one is eligible for moral assessment; in which responsibility resides; or (equivalently) to which our moral assessment attaches. Call this the focal act. The crucial point is that one may be responsible in acting, in a completely different sense from how one may be responsible for an outcome or event (or even 'for an action', considered as a mere outcome or event, as opposed to a focal act). HS runs together 'focal actions' and 'acts-as-events' in a way which causes her to seriously misconstrue the issue at hand, or so I claim.]
Another way to see this point is to note that it doesn't seem to make any difference for HS's cases who ends up performing the unwitting bad act. She is talking about blaming Adam for Bob's death in the exact same way that we would blame Adam for Bob's death if he had negligently misplaced Cid's glasses, and Cid subsequently crashed into Bob. That is, we're blaming Adam for the outcome of Bob's death, and not (in any further sense) the act of killing him. In either case, the act of Adam's to which our blame attaches - the focal act - is the reckless 'benighting' act of depriving a driver of his glasses. This is clearly to change the subject, if what we're interested in is whether ignorance excuses (blocks blame from "attaching to") the unwitting act (as a locus). On the other hand, if we're interested in whether Adam is blameworthy, in his negligence, for the event of Bob's death, any ignorance in the "later" actor -- whether Cid or Adam himself -- is just obviously irrelevant.
Simply put: we are responsible, though (or 'in') a focal action, for various outcomes. If those outcomes are bad, there's a prima facie case for thinking the agent, in acting as they did, blameworthy. We may then ask whether there are any 'excuses' or defeaters for this presumption. These are things that may excuse the agent's action, rendering them no longer liable (again, in so acting) for various consequences. One possible excuse is ignorance. But note: By this it is not meant that if the agent becomes ignorant consequently from their act, this somehow blocks the agent from liability for any further downstream consequences of their focal act. That would be daft. No, the relevant 'ignorance' (ignorance that is eligible to excuse an agent's action) must be present in the act itself -- i.e. the act must have been done "from ignorance". It is ignorance concurrent with the focal act -- the exercise of agency in virtue of which the agent is prima facie eligible for moral assessment (positive or negative depending on, amongst other things, the consequences resulting from the act).
So, if we are considering complicated examples in which one action has as its causal upshot another act's performance, we need to be clear if the former is being treated as the focal act, and the latter as a mere event. Because if we're interested in whether ignorance (e.g. of some feature or outcome) excuses the agent's action, we had better be talking about ignorance that is concurrent with the focal action, and not ignorance that is concurrent with the mere downstream event. But this is precisely what HS fails to do. Her examples all concern cases of ignorance downstream of the focal act. As such, they are not even formally eligible to serve as excuses for the agent's action. Her very question is ill-formed.
P.S. My follow-up post considers more appropriate cases, i.e. of culpable ignorance concurrent with a focal act.
* I should note that 'culpable ignorance' is being used here in a potentially misleading way. HS really means something more like "self-inflicted ignorance", or "ignorance for which one is responsible in virtue of a prior culpable act". But that's just not the same thing as ignorance that is culpable or unreasonable in itself -- as I emphasize in my follow-up post. A 'snapshot theorist' may hold, as I do, that self-inflicted but intrinsically reasonable ignorance is indeed wholly exculpatory in the relevant sense, whilst intrinsic or 'synchronically culpable' ignorance is no excuse.
** [I owe the basic 'misdiagnosis' idea to Liz. The arguments - and broader conclusions - are my own.]