In essence the question of standing is whether the litigant is entitled to have the court decide the merits of the dispute or of particular issues. Standing doctrine embraces... the general prohibition on a litigant's raising another person's legal rights, the rule barring adjudication of generalized grievances more appropriately addressed in the representative branches, and the requirement that a plaintiff's complaint fall within the zone of interests protected by the law invoked. The requirement of standing, however, has a core component derived directly from the Constitution. A plaintiff must allege personal injury fairly traceable to defendant’s allegedly unlawful conduct and likely to be redressed by the requested relief.