There is still no answer to many scientific questions and there exists an uncertain degree of knowledge with regard to major disciplines. The physical and behavioural sciences such as psychology and economics, which are so frequently looked to for certitude, do not always come up with clear cut answers; and unsubstantiated theories often disguise a lack of knowledge.
While one category of ignorance applies to what is not known, another category applies to the inability to assemble all the facts needed. For example, although there may be considerable understanding of the effects of single policies on single objectives, where multiple and sometimes conflicting effects and objectives of programmes and policies exist the processes for evaluating all these may be too complex, so that decisions are made in ignorance of all the relevant data.
Another type of ignorance allows for the knowledge to exist and also the capability and means to acquire it, but the will to do so is not present. Unwillingness to look at the facts constitutes intellectual bias. An emotional bias has the same effect, such as identification with a particular set of interests whether they are national, political, economic, ideological or religious. In the latter case, a tenet of Roman Catholic theology, for example, describes those who will never embrace Christianity due to their heredity, upbringing or environment, as 'invincibly ignorant', which aptly describes the 'closed' mind in any situation.
Ignorance can often be propagated under the guise of balanced debate. For example, the common idea that there will always be two opposing views does not always result in a rational conclusion. This was behind how tobacco firms used science to make their products look harmless, and is used today by climate change deniers to argue against the scientific evidence. “This ‘balance routine’ has allowed the cigarette men, or climate deniers today, to claim that there are two sides to every story, that ‘experts disagree’ – creating a false picture of the truth, hence ignorance.”
The internet is helping propagate ignorance – it is a place where everyone has a chance to be their own expert, which makes them prey for powerful interests wishing to deliberately spread ignorance. While some smart people will profit from all the information now just a click away, many will be misled into a false sense of expertise. Other people's opinions go a long way toward correcting our own imperfections, as our own imperfect expertise helps to correct their errors.