In United States v. Carolene Products Co., Justice Stone suggested by indirection that there may be narrower scope for operation of the presumption of constitutionality when courts are called upon to determine the validity of statutes directed at particular religious . . . or national . . . or racial minorities. \u27 In such cases, he explained, prejudice against discrete and insular minorities may be a special condition, which tends seriously to curtail the operation of those political processes ordinarily to be relied upon to protect minorities, and which may call for a correspondingly more searching judicial inquiry. \u27 Forty years later, that cautious suggestion has ripened into an attitude. The fact that legislation bears heavily...