2A is about an individual's RKBA for self defense. Congress has all the authority it needs for the
militia in Article I, Section 8, clauses 15 & 16.
SCOTUS acknowledged in Heller both opinion and dissent that individuals have a natural, inherent, inalienable/unalienable right to keep and bear arms for self-defense.
The main difference was the opinion said that right was in the Second Amendment and the dissent disagreed but recognized the right in the extract below.
The dissent by recognizing the right but asserting it was not an enumerated right protected by the Second Amendment meant the right was an unenumerated right protected by the Ninth Amendment.
The parallels between the Second Amendment and these state declarations, and the Second Amendment ’s omission of any statement of purpose related to the right to use firearms for hunting or personal self-defense, is especially striking in light of the fact that the Declarations of Rights of Pennsylvania and Vermont did expresslyprotect such civilian uses at the time. Article XIII of Pennsylvania’s 1776 Declaration of Rights announced that “the people have a right to bear arms for the defence of themselves and the state,” 1 Schwartz 266 (emphasis added); §43 of the Declaration assured that “the inhabitants of this state shall have the liberty to fowl and hunt in seasonable times on the lands they hold, and on all other lands therein not inclosed,” id., at 274. And Article XV of the 1777 Vermont Declaration of Rights guaranteed “hat the people have a right to bear arms for the defence of themselves and the State.” Id., at 324 (emphasis added). The contrast between those two declarations and the Second Amendment reinforces the clear statement of purpose announced in the Amendment’s preamble. It confirms that the Framers’ single-minded focus in crafting the constitutional guarantee “to keep and bear arms” was on military uses of firearms, which they viewed in the context of service in state militias.