A contradiction in Schmitt's theoretical approach to law?

Much of Schmitt's early Weimar-era works focus on the socially deleterious effects produced by the application of the theory of legal positivism to legal practice. This problem touches on a central question of legal theory: to what extent do theories of law affect the practice of law? From a practical standpoint, I believe Lon Fuller answers the question adequately when he asserts that, "in human affairs what men mistakenly accept as real tends, by the very act of their acceptance, to become real." 1

But for Schmitt the issue does not end with Fuller's assertion. Schmitt's intellectual foundation is partially comprised of various forms of German lebensphilosophie, which conclude in different ways that our theories about the world are formed by pre-conceptual human activities and experiences in concrete life. Informed by this perspective, Schmitt often speaks of concrete political and social situations generating theories of law that project rationalizations onto institutions formed out of pre-conceptual concrete life.

Thus, for example, legal positivism is a theoretical derivation from the institutions and political stability that emerged in 19th-century Europe. Legal positivism must therefore be something appropriate for the historical "concrete order" that it was generated for. How does this square with Schmitt's argument that the application of legal positivism is socially dangerous?

Schmitt argues elsewhere that the problem of legal positivism emerges when the institutional order that generated the theory falls away, leaving only the theory but not the institutions. When jurists in the new epoch proceed in accordance with a legal positivist understanding of the law, they make grievous errors which have immoral consequences because the current social order is not fit for legal positivism. Schmitt therefore also believes that theory can affect and modify the concrete life of human institutions. But how could this be if the concrete existence of humans generates appropriate theories to explain and justify the social shape that it forms?

1. Lon L. Fuller, "Positivism and Fidelity to Law -- A Reply to Professor Hart," 71 Harvard Law Review 630 (1958)