While the need for state militias has not been a matter of significant public interest for almost two centuries, that fact should not obscure the contemporary concerns that animated the Framers.(emphasis added). Stevens uses this point to argue that state sovereignty issues are at the forefront of the purpose of the 2nd Amendment (of course, D.C. is not a state), and that the framers were singularly concerned about a national standing army replacing state militias (which has happened anyway).
But the more interesting point is his chosen method of interpretation: Originalism. This is not his usual point of view. Could you see him using this rationale for the enforcement of the death penalty? The framers were probably not "animated" by many of the methods of execution that are not considered suitable today (e.g., hanging, firing squad) in creating a ban on "cruel and unusual punishment," but I doubt you'd see Stevens upholding such punishment on the basis of what "animated" the framers.