In politics, it is almost always used as a pejorative label, but some political movements have raised it to an ideal, for instance the Know-Nothings of the 19th century United States and some peasant and agrarian movements. This is usually simply a rejection of academia and professions and other power structures that are based on knowledge. A modern expression of this is the so-called "common sense conservative" who celebrates being unable to understand arguments for left-wing politics or green politics that violates his many pre-existing assumptions. This is a very common way to support a regime of property rights for instance, as one claiming ignorance of how property was acquired (say by force or fraud) can also claim righteous indignation when his rights in it may be curtailed.
Despite the admonition in some faiths that ignorance is bliss, some religions are particularly adamant that it does more harm that good. For instance, Islam views ignorance as a particular and unique evil that can and should easily be dispelled: "Seek knowledge, even as far as China." - Muhammad
In a society with a strong hierarchy or caste system, ignorance of the concerns of those one does not work or deal with directly may aid labour specialization, reduce jealousy and dissent, and otherwise serve the interests of social harmony. In such a society, control of any mass media tends to be carefully controlled, and one tends to perform one job for life.
There are few or no ethical traditions today that emphasize plain ignorance as a value. However, certain ideologies persist that find it useful or desirable.
When cultures meet however, ignorance can become particularly dangerous, as one's inability to comprehend the customs of others can lead to offense and thus harm. When Europeans began colonization of North America, there were many incidents in which conflict arose from unintended misunderstandings. There were of course also many bona fide clashes of values and bigotry - a particularly noxious byproduct of ignorance being racism and intolerance.
What is different is by and large seen as dangerous and threatening in animal cognition.
In humans, ignorance of another's lifeways or circumstances, failure to empathize with his or her experience, is cited in political science as one of the most common causes of conflict. Thus to build common experiences, e.g. to plant olive trees in regions where they have been torn up due to conflict, and learn at the same time, is thought to be one of the most effective forms of education and also of peacemaking. Crick's political virtues emphasize this kind of skill and activity where it is difficult or impossible to actually share perspectives.
See also: trust, doubt, truth, list of ethics topics