Over at Balkinization, Brian Tamanaha offers this very good response to Richard Posner's claim that many court of appeals cases are and should be decided based on the judges' normative views. It seems to me that this is Tamanaha's key point:

Posner has in effect given us two tests to be used together: if the law is clear, the judge must follow it, but if the law is unclear (which he says happens a lot), then the judge can rule in favor of what the judge deems reasonable, unless that particular outcome is clearly prohibited by the law. Sandwiched between these two tests is the large body of cases in which the law is less than clear, but one result is more legally compelling or defensible than any alternative interpretation. Unlike pragmatic adjudicators, who in these cases will decide for the reasonable result (as determined by their own lights) unless it is clearly ruled out, judges committed to following the law will feel duty-bound to render the most legally compelling decision.