Prof. Mark Liberman (Language Log) has an interesting post on usage debates and political debates; you should read the whole thing, but here’s an excerpt:
[T]he insistence on regulation by prescriptive “rules”, in whatever relationship to the direction of linguistic history, is another interesting inversion of the standard political metaphors as applied to matters of usage. Consider this passage from Friedrich Hayek, Law, Legislation and Liberty, Volumes 1: Rules and Order, p. 10-11:
[Constructivist rationalism] produced a renewed propensity to ascribe the origin of all institutions of culture to invention or design. Morals, religion and law, language and writing, money and the market, were thought of as having been deliberately constructed by somebody, or at least as owing whatever perfection they possessed to such design....
Yet ... [m]any of the institutions of society which are indispensible conditions for the successful pursuit of our conscious aims are in fact the result of customs, habits or practices which have been neither invented nor are observed with any such purpose in view....
Man ... is successful not because he knows why he ought to observe the rules which he does observe, or is even capable of stating all these rules in words, but because his thinking and acting are governed by rules which have by a process of selection been evolved in the society in which he lives, and which are thus the product of the experience of generations.
It would be hard to find a better statement of the descriptivist attitude towards linguistic norms.
But Hayek is using a general discussion of “all institutions of culture” to argue for a libertarian approach to economic and social policy, avoiding central planning and minimizing coercive regulatory intervention. Hayek was “one of Ronald Reagan’s favorite thinkers” and an important influence on Margaret Thatcher — I think it’s fair to associate these attitudes with the right-hand side of the political spectrum over the past half-century or so.
Projecting political, social, and cultural philosophies onto a single dimension necessarily yields odd juxtapositions. But if we insist on doing it, we should try to be clear about the process and the results. Today, most people who know what the words mean would align “descriptivism” and “prescriptivism” as left and right respectively, I suppose because they associate the elitist and authoritarian aspects of prescriptivism with the political right. But the right has no monopoly on class-consciousness or on coercion. And in this case, I feel that the natural projection falls in the opposite direction.