As many have observed, to a large extent the legal realists created a straw man with their caricature of nineteenth century legal scholarship. Additionally, the realists substantially changed the self-understanding of lawyers. (For an accessible discussion of the effects of legal realism on the practicing American lawyer, read Mike Schutt's Oliver Wendell Holmes and the Decline of the American Lawyer: Social Engineering, Religion, and the Search for Professional Identity, 30 Rutgers L.J. 143 (1998)). In any event, their legal agenda "just happened" to coincide with the political agenda of early twentieth century Progressivism. In fact, many legal realists served in the presidential administration of Franklin D. Roosevelt.
In any event, the deconstructive program of the legal realists could be turned against them as easily as they had deployed it against their nineteenth century forbears. Reading through James Gordley's, "The Jurists: A Critical History" (previously noted here), I came across this critical observation from a leading second-generation legal realist, Felix Cohen:
We have heard a good deal, in the last twenty years [Cohen wrote in 1938], of the need for examining the consequences of legal rules, but "sociological jurisprudence" [a subset of legal realism] remains in large part a pious program rather than a record of achievement. At the root of this failure is the lack of any definite criterion of importance which will dictate which of the infinite consequences of a legal rule or decision deserve to be investigated. Such a criterion of importance can be supplied only by an ethical system. But thus far, none of the advocates of sociological jurisprudence believe in any ethical system, or, if they do, no word of it is spoken before company.Although he didn't know it at the time, Cohen was identifying legal realism as another form of emotivism.