In his book Does Accent Matter? The Pygmalion Factor, John Honey writes that public school attendance or an RP [Received Pronunciation] accent were among the main criteria for being a British army officer in the world wars of last century. (Actor Dirk Bogarde is said to have attributed his promotions in WWII to his accent.) According to Honey, carnage in the trenches led to a relaxation in the requirement for an RP accent, and men were commissioned “whose voices betrayed their promotion from the ranks”.
Such was the prestige of an RP accent that its lack in these newly promoted officers — the “temporary gentlemen” of Pat Barker’s historical fiction — was apt to invite automatic disrespect from certain quarters. When one such officer inspected the cadets at a public school in Lancing in 1919, Evelyn Waugh (then in his mid-teens) helped organise the dropping of rifles to demonstrate against the officer’s regional form of speech. As a collective gesture it was perhaps more powerful than a Waugh of words would have been.
Honey describes the role schools played in creating a consensus that certain accents were authoritative, while others — whether from the mouths of students or teachers — were shameful:
There is little evidence that, in boys’ public schools at least, [RP] was systematically taught. New boys with local accents were simply shamed out of them by the pressure of the school’s ‘public opinion’. The prep schools, having pupils at an earlier, more formative age, were very important in this respect. In the decades immediately following 1870 there was a time-lag before non-standard accents died out among masters (and indeed headmasters) in the leading public schools. New appointees could be, and were, screened for accent. The boys’ reaction to that minority with ‘suspect’ accents who got through this screening depended upon their general effectiveness as teachers: a weak disciplinarian would find that his accent became another stick with which they would beat or bait him. In a popular man, respected for his teaching or sporting gifts, mildly non-standard speech forms were tolerated — even humoured — as part of the idiosyncrasies of a ‘character’.
As Orwell put it in Politics vs. Literature: “public opinion, because of the tremendous urge to conformity, is less tolerant than any system of law”. Donning my biologist’s hat for a moment, I would say that conformity can be a powerful motivator of behaviour because it serves the structure and survival of a group. This instinct, which can manifest with great cruelty (ridicule, humiliation, isolation, and so on), probably serves an adaptive purpose. It binds a social group, strengthening its cohesion by dismissing outliers (or demanding that they cooperate), and thereby fostering a more effective and efficient system. It’s not pretty, but it’s very mammalian.
Update: There’s further discussion about this at Language Hat.