The “ideal speaker-listener in a completely homogeneous speech community” which certain varieties of phonological theory have been so keen on invoking is, and as far as can be ascertained always has been, a figment of such theorists’ wishful thinking. No speech community is ever homogeneous, and it has never been clear what properties would suffice to characterise a speaker/hearer as ideal. The construct has simply been a convenient way of disregarding socially motivated (or at least socially relevant) variation, in the pursuit of a more psychologically oriented view of spoken language.
The observable and undeniable lack of homogeneity in the speech community is, however, not something to be regretted or wished away, because it is (on some views at least) the very object which linguists are best suited to analysing. “Indeed,” as Foulkes and Docherty point out in a recent article,
“the interweaving of sociophonetic and linguistic information in speech is so complete that no natural human utterance can offer linguistic information without simultaneously indexing one or more social factor.”
(Roughly the same point was made by Labov when he commented, “I have resisted the term sociolinguistics for many years, since it implies that there can be a successful linguistic theory or practice which is not social.”)
It’s hard to know whether the pursuit of a psychological model necessarily has to involve neglecting a more socially grounded one, or if it just so happens that the kind of psychology which the most vocal theoretical phonologists of the past several decades were interested in is one that doesn’t (cannot?) engage with sociophonetics. Either way, the exclusion of sociological information from the study of spoken human communication is both unwarranted and counter-productive – there must be a better way of doing things.
Foulkes & Docherty (2006), ‘The social life of phonetics and phonology.’ Journal of Phonetics 34: 409-438