injury requirement ensures that issues will be resolved "not in the rarified atmosphere of a debating society, but in a concrete factual context." Valley Forge Christian College v. Americans United for Separation of Church and State, inc., 454 U.S. 464, 472, 102 S.Ct. 752, 70 L.Ed.2d 700 (1982). 18 redressable by a favorabl