Here is an increasingly accepted post-September 11 view about racial and national origin profiling (i.e., "profiling") in law enforcement: it may be troubling but its use should depend on the context (Part I). In other words, legislatures, courts, and executive officials should weigh the costs and benefits of using a particular law enforcement policy (i.e., profiling) in a given context (i.e., the war on terrorism). The problem is that this idea suffers from massive conceptual and practical difficulties, underscored by the fact that terms like cost, benefit, and terrorism are not self-explanatory. Yet the intuitive appeal of some anti-terror policies - including profiling - can result in a sort of "plausibility principle," where legislatures, courts, and others often consider the merits of law enforcement strategies merely on the basis of whether such policies have a plausible justification (Part II). The problems that arise with general discussions of profiling are not likely to be solved by judicial review of individual profiling policies because the relevant constitutional doctrines - under equal protection, due process, and the Fourth and First Amendments - do little to regulate law enforcement's decisions to investigate and prosecute (Part III). Which means that to decide whether profiling itself makes sense, we must consider the dynamics driving law enforcement's use of discretion. At least one aspect of this should raise concern - that statutory and other legal changes increase law enforcement's flexibility not only to choose whom to investigate, but what sorts of methods to deploy, including troubling tactics such as extended detention of immigrants, secret searches, or wiretaps (Part IV). Changes in the judicial regulation of discretion are possible but unlikely, and data will continue to be scarce. All of which makes it hard to accept even a principled "context-dependent" case for legitimizing profiling in the war on terror, and highlights the disconnection between asserted justifications for particular enforcement strategies and the likely performance of enforcement systems.