[T]he government cannot be expected to make assurances regarding individuals who file a suit in a context such as this, based solely upon their allegations and without knowledge of other facts that might be relevant to determining whether the individuals fall within the scope of the detention authority affirmed by section 1021.

. . . .

In the context of this case, it is particularly inappropriate to shift the burden to the government to disprove a plaintiff ’s speculative fear of future harm. To require the government to evaluate and declare whether or not a statute affirming the authorization of the use of force—here, in the form of detention—during an armed conflict would apply to specific individuals for specific conduct would place the government in an untenable position: the government would be inundated with copycat suits and be forced to give what would be advisory opinions to countless individuals regardless of whether they have shown a reasonable fear of enforcement. Tr. 268-69. The government cannot be required to define the boundaries of its authority by giving ex ante assurances to individuals in this manner, especially to individuals who lack a sufficient “personal stake in the outcome of the controversy . . . to justify exercise of the court’s remedial powers on [their] behalf.” Warth v. Seldin, 422 U.S. 490, 498-99 (1975).