Good journalism, even when practiced for profit, is a public service. Lately, however, top news organizations, frustrated by criticism from on high, have taken to describing their mission as more of a crusade. The Washington Post, in the public eye more than usual this month with the opening of “The Post” - a film about the paper’s 1971 decision to publish the so-called Pentagon Papers, which revealed a secret government analysis of the failing Vietnam War-adopted a new slogan last year.