Those people talk funny
Coming to a plain in Shinar, they made bricks to build a tower to reach heaven. God, seeing this, was irritated: "Look, they are one people, and they have all one language; and this is only the beginning of what they will do; nothing that they propose to do will now be impossible for them. Come, let us go down, and confuse their language there, so that they will not understand one another’s speech." Thus, at Babel, the one language of human beings was broken into many languages.
Genesis has one version of the origin of the confusion of tongues. Another can be found in Nicholas Wade's recent book, Before the Dawn: Recovering the Lost History of Our Ancestors. It wasn't pride or striving to rival God; it was hostility.
Wade ties together archaeological and anthropological information with recent research in genetics to present theories about the evolution of modern humans. If, as Wade proposes, a small group of no more than a couple of hundred modern humans, speaking one language, left Africa 50,000 years ago to become the ancestors of all living humans, what happened to that language?
His answer is that our early ancestors split into small hunter-gatherer groups as population grew. Because hunter-gatherers tend to isolate themselves into small, clearly defined territories and treat competing groups with hostility, it was inevitable that language would evolve into dialects that "serve to distinguish friend from foe."
That is, "The mutability of language reflects the dark truth that humans evolved in a savage and dangerous world, in which the deadliest threat came from other human groups. … Even if the original settlers all speak the same language, dialects quickly evolve in each group’s territory, as a badge of identity and a defense against outsiders."
And even once humans evolve into settled, agricultural and industrial societies, those badges of identity continue to be useful.
The relative isolation of Appalachia and the common heritage of the first Scots-Irish settlers combined to preserve vocabulary and pronunciation from 18th-century British English in the Southern Mountain dialect of my native Kentucky. (That vocabulary and pronunciation still identifies who is native and who is an outsider.)
Perhaps here we can see why pronunciation and usage stir strong feeling. We may no longer be members of bands warring with neighbors who want to poach our fruit and steal our women, but we continue to have a strong need to identify with a group and identify strangers whose interests may be contrary to ours. Group identification comes with positive and negative aspects. Language identifies people by education, by ethnic origin, by social class, by many of the markers that determine who the People Like Us are. The People Who Are Not Like Us become those on whom we can project our fears, our anger, our contempt.