Granting terrorists legitimacy in any way, shape, or form is a very bad idea, and yet the Bush administration regularly does so by invoking the language of a "war on terrorism." War is fought by belligerents and belligerents, whether fighting on behalf of states or non-state entities, have equal rights on the battlefield. Belligerents, in fact, have the right under international law to kill other belligerents. When they kill non-belligerents (civilians or those who are hors de combat), they have committed a war crime. But not all killing by belligerents is criminal in nature.
Conversely, those who kill intentionally without belligerent status are criminals (except in very limited circumstances of self-defense)--period. Societies based on law single them out and punish them as criminals. To call criminals "belligerents"--implicitly conceding that there are some circumstances in which they might kill without criminality--is a mistake. Yet that's exactly what we do every time we suggest that terrorists are our opposite numbers in the "war on terrorism."
In today's New York Times, David E. Sanger writes about the debate over the "war on terrorism" trope:
Soon after the British police announced last week that they had broken up a plot to blow up aircraft across the Atlantic, President Bush declared the affair "a stark reminder that this nation is at war with Islamic fascists."
British officials, on the other hand, referred to the men in custody as "main players," and declined to discuss either their motives or ideology so that they would not jeopardize "criminal proceedings."
The difference in these initial public characterizations was revealing: The American president summoned up language reaffirming that the United States is locked in a global war in which its enemies are bound together by a common ideology, and a common hatred of democracy. For the moment, the British carefully stuck to the toned-down language of law enforcement.
Sanger presents a much more balanced view of the issue than I do, so read what he says about it.