Wittgenstein warned against the “craving for generality”: the mistaken desire to find uniformity where there is only diversity. Thus philosophers are apt to suppose that all words are names, all sentences are assertions, and all states of mind are experiential—despite a heterogeneity that is evident to unbiased inspection. In a word, they overgeneralize, often based on preconceived ideas. Hence his admonition: “Don’t think, look!” Evidently this is a natural tendency of the human mind, which we need to resist. At roughly the same time Nabokov was inveighing against what he called “generalities”, particularly on the part of historians. He begins his 1926 essay “On Generalities” with these words: “There is a very tempting and very harmful demon: the demon of generalizations. He captivates human thought by marking every phenomenon with a little label, and carefully placing it next to another, also meticulously wrapped and numbered phenomenon.” He goes on to excoriate historians for indulging in the tendency to find spurious similarities, thus erecting oversimplified “epochs”, “ages”, and “periods”. Walter Lippmann in his 1922 book Public Opinion first introduced the word “stereotype” in its modern sense (before that it was used in the printing industry), i.e. as connoting a tendency towards social overgeneralization and simplistic grouping. Here again the fault lies in not looking, observing and recording, but instead relying on overly simple and homogenizing ideas. Thus, according to these three thinkers, we find people mistakenly supposing (a) that all words are names, (b) that all authors of a certain period are to be classified as (say) Romantics, and (c) that all people of a certain culture or ethnic group have such and such characteristics. In each case we have what we would now call stereotypical thinking; and the problem with it is that it is false and can be very harmful. Yet people keep on doing it: they keep on ignoring the facts, the details, and the individualities, preferring instead the meritless generalization, the lazy grouping, and the prejudiced espousal of alleged commonalities. In some cases this is clearly deplorable, contemptible, and just plain stupid; but human beings seem intent on indulging their craving for generality no matter the cost. It is as if they have a demented love of identity.
I emphasize the pervasiveness of the phenomenon because social stereotyping is not some isolated and unique failing: it is built into the fabric of human cognition (which is not say it is incurable). It is entirely possible to stereotype animals, fictional genres, popular music, athletes, professors, and even rocks. Overgeneralization and preconceived ideas are the stuff of weak minds. Today there is a tendency to stereotype certain individuals as “powerful white males” and then run away with all sorts of misguided and erroneous ideas about this supposed class. Philosophers and other academics are not immune to this, shameful though it may be.  Often it is done in order to advance a certain political agenda, but it is also just plain lazy thinking and good old-fashioned stupidity. It needs to be identified for what it is and condemned in the strongest terms. Stereotyping is never an acceptable way to think (sic). No doubt it has its biological origins in a need to economize on time—to make thinking more efficient. Fine, but not at the cost of accuracy and justice: because stereotyping people is a vicious and idiotic habit. It needs to be stamped out (is jail time too much to ask?). Children need to be educated strenuously in its fatuity and danger. It has to go.
Under what circumstances does stereotyping take hold? I think it’s when people feel overwhelmed by the sheer diversity of the world (of course, there can also be emotional reasons, meme transmission, indoctrination, imitation, and the like). If the world is perceived as intolerably complex, people will want to simplify it and make it more manageable: it’s easier to think that every word is a name, every writer from a certain period belongs to a certain “school”, and that every person of a certain appearance is thus-and-so (generally a negative thus-and-so). This is no doubt understandable, but it is not commendable, or even forgivable. In a society like America, which has a very diverse population, the urge to oversimplify and classify is particularly strong: it’s just easier to try to subsume everyone under certain crisply defined categories. The task of education should be to combat this cognitive weakness. This is a type of therapy (as Wittgenstein recommended therapy for the disease of philosophical overgeneralization): people need to be cured of their stereotyping, as if it were a disease. In fact, it really is a type of mental disease—just an exceptionally common one (like the common cold). The first step here is to get a proper sense of its pathological character, its demonic morphology, its onset and progression. A stigma needs to be firmly attached to it. As it is stereotyping gets reinforced and solidified, but it needs to be exposed and ridiculed. But don’t count on academic philosophers to do any of this good work; they seem as prone to it as anyone else, sad to say. It really is a problem, despite its obvious malignity. 
 In fact academics are professionally prone to it, because they make a living erecting generalizations, producing taxonomies, and promoting theories; they would feel thwarted if restricted to reporting the facts. Recalcitrant facts are the enemy of the ambitious theoretician.
 This is generally recognized, though people seem oddly blind to it in themselves (they just have betterstereotypes). I am attempting here to describe it succinctly and clearly so that its malign presence can more readily be eradicated.