Let's consider some possible definitions of culpable ignorance.
(1) It's ignorance that's within our power to avoid, and that results from a failure to comply with our epistemic duty to become informed about something (when we have such a duty). Because we have some control over whether or not we're culpably ignorant, we can be held morally responsible for being so. A distinction can thus be made between ignorance for which we're responsible (culpable ignorance) and ignorance for which we're not responsible (non-culpable ignorance).
(2) Culpable ignorance is ignorance for which there's no excuse, and for which there are harmful or undesirable consequences that could have been avoided or anticipated. It can be argued that simply being culpably ignorant is harmless if no negative consequences result from that ignorance. (It can also be argued that ignorance of any kind is intrinsically harmful, but this seems somewhat implausible.) From a consequentialist perspective, simply not knowing something we should have known may not make us culpably ignorant unless some harmful or undesirable consequences result from that ignorance. The extent of our culpability for our ignorance may depend on the wrongness or inappropriateness of the actions that result from that ignorance, as well as the gravity and extent of their negative consequences.
(3) Culpable ignorance is ignorance in cases where we "should have known better" or "should have realized" that relevant facts or conditions needed to be considered.
(4) It's also ignorance where we failed to take due regard of, or pay sufficient attention to, relevant facts or conditions.
(5) It's also the spreading or promulgation of falsehoods and misinformation, without any regard for the veracity of that information or the consequences of spreading such falsehoods and misinformation.
Ignorance alone isn't culpable, if there's some excuse for it. The ignorance must be inexcusable rather than excusable, deliberate rather than inadvertent, or intentional rather than unintentional, if it's rightly to be held as culpable. However, if an individual refuses to reexamine or reevaluate their beliefs despite evidence that those beliefs may be mistaken or in need of better justification, then they may be held blameworthy for their refusal to reexamine or reevaluate their beliefs. Similarly, if an individual takes an action for which some knowledge of relevant facts is necessary in order to determine the action's rightness or appropriateness, and they willfully refuse to inform themselves of those relevant facts, then they may rightly be held responsible for any negative consequences of that action.
We may be culpably ignorant for not knowing something (such as the rightness or wrongness of a particular action) if (1) we should have known about that thing (or should have known that we didn't know about that thing), and (2) as a consequence of that ignorance, we (a) do what we shouldn't have done or cause others to do what they shouldn't have done, or (b) don't do what we should have done or cause others not to do what they should have done. If our actions or non-actions in such cases cause negative consequences for ourselves or others, then we may rightly be held blameworthy for those actions or non-actions.
Holly Smith (1983) argues that the concept of culpable ignorance must be restricted to (1) cases in which an individual believed they were acting justifiably, and (2) cases in which they were not acting precipitously. Thus, culpable ignorance involves an initial "benighting act" for which the individual is culpable and in which the individual fails to improve (or positively impairs) their initial cognitive position, followed by an "unwitting wrongful act."1
Niels de Haan (2020) argues that culpable ignorance may in some cases be irreducibly collective (not attributable to a single individual). While it might not be fair in some cases to expect an individual to have avoided their ignorance of a particular fact, it might be fair to expect the group to which they belong to have collectively avoided its ignorance of that particular fact.2 In such cases, the group, rather than the individual, is culpable (or at least the individual is culpable only insofar as they are a member of that group). de Haan notes that an individual's (or group's) culpability for not knowing something may also imply they could reasonably have been expected to take measures to remedy or avoid that ignorance.3
Alexander F. Sarch (2014) explains that when someone is willfully ignorant of some fact (when they deliberately avoided learning whether the fact in question obtained), they may be held culpable for that ignorance. For example, in cases where a defendant is charged with a crime, and the defendant was willfully ignorant of some fact, they may, according to the "willful ignorance doctrine," be found to be culpable on the ground they were willfully ignorant of the relevant fact.4
Culpable ignorance may include willful ignorance (the deliberate rejection of knowledge or the deliberate avoidance of measures to become informed about something), but not all culpable ignorance is willful, insofar as it may in some cases be due simply to a lack of diligence with regard to measures to become informed about something (in cases where there is a duty to become informed about that thing), rather than deliberate avoidance of those measures.
Jason B. Freeman (2022) defines willful blindness as "an attempt to avoid liability for a wrongful act by intentionally failing to make reasonable inquiry when faced with the suspicion or awareness of the high likelihood of wrongdoing." He also says, "It is a deliberate attempt to keep one's "head in the sand" when faced with information or facts that create a suspicion or awareness that there is a likelihood of wrongdoing."5
The Law Library of American Law and Legal Information at law.jrank.org defines culpable ignorance as "the lack of knowledge or understanding that results from the omission of ordinary care to acquire such knowledge or understanding."6
What's the relation between willful ignorance and denialism? They may be closely related to or associated with each other, but they aren't the same. Willful ignorance may involve a failure to be acquainted with relevant facts, while denialism may involve an acquaintance with relevant facts, but a failure to recognize those facts as facts. For example, denialism may involve denial of such facts as the link between HIV and AIDS, the link between greenhouse gas emissions and climate change, and the efficacy of vaccines in preventing transmissible diseases such as polio, measles, and COVID-19.
Charles W. Mills (2007) describes "white ignorance" as a group-based cognitive phenomenon that has epistemic, moral, social, and political implications. It's based on a system of white privilege in which white racism plays a significant causal role. It's also based on white normativity, i.e. on the centering of whiteness as a constitutive norm, while the experience of blacks and other people of color is marginalized. One of its functions has been to protect those who for racial reasons have needed not to see or know about the black or brown people in their midst.7
Annette Martin (2021) presents three alternative accounts of "white ignorance," as (1) a willful ignorance about racial injustice (the "willful ignorance view"), (2) an ignorance resulting from social practices that distribute faulty cognitive resources, e.g. by accepting faulty norms of reasoning about race (the "cognitivist view"), and (3) an ignorance resulting from a social process that systemically gives rise to racial injustice (the "structuralist view").8
Examples of white ignorance (sometimes guised as "color blindness") include blindness to acts of racial injustice, blindness to racially discriminatory laws or policies, and blindness to structures of racial inequality.
FOOTNOTES
1Holly Smith, "Culpable Ignorance," in The Philosopher's Annual, Vol. VI, 1983, 243-271.
2Niels de Haan, "Collective Culpable Ignorance," in Thought: A Journal of Philosophy, Vol. 10, Issue 2, 2021, p. 99.
3Ibid., p. 100.
4Alexander F. Sarch, "Willful ignorance, Culpability, and the Criminal Law," in St. John's Law Review, No. 4, Vol. 88, 2014, 1022-1101.
5Jason B. Freeman, "Willful Blindness and Corporate Liability," 2022, online at Freeman Law, https://freemanlaw.com/willful-blindness-and-corporate-liability/.
6Law Library of American Law and Legal Information, "Culpable," 2022, online at https://law.jrank.org/pages/5914/Culpable.html
7Charles W. Mills, "White Ignorance," in Race and Epistemologies of Ignorance, edited by Shannon Sullivan and Nancy Tuana (Albany, State University of New York Press, 2007, pp. 13-28.
8Annette Martin, "What is White Ignorance?" in The Philosophical Quarterly, Vol. 71, Issue 4, October 2021, 864-885.