One interpretation of the moment in Kant's presentation on "radical" (fundamental) "evil" where he asserts the universality of the predicate, vs. humanity, is that being finite is somehow what exposes us to this universal predication. Without granting that proposal in letter, in spirit I will suggest that the theory of radical evil is recursively explanatory, namely radical evil is something to do with our knowledge of good and evil, the way that this knowledge does or does not "work." Kant might be recapitulating an earlier debate, over synderesis vs. total depravity (is there an incorruptible method of moral knowledge or are all polluted, even the most abstract one?), in a more definite form.
Now Kant never, to my knowledge(!), comprehensively explains the role of intuitions and concepts in the exact form of moral knowledge. In fact, his fact of reason is said to be synthetic a priori but not intuitively discerned. But let us suppose that in a system of metaethics where transcendental freedom is constitutive, it would be a postulate of pure practical reason that our very form of ethical knowledge would be subject to our choice. Not our finitude, but that we chose to limit our moral knowledge to discursive more than real intuitive cognition, is what shows us all to be infiltrated by radical evil, for no one on the Earth has ever provably had the ability to just "know" what is right and wrong, good and evil, "just by looking at it" or what. And so yet in our finitude's shadow we see what darkness of sin is casting that shadow...
Besides objecting to the idea that intuitions are for the most part lacking in unique evidential value for moral assertions, one might object that there would be nothing better in having real Moore-Ross (or whoever) intuition anyway. However, wouldn't it be easier to answer moral questions if we did have such intuition? What for Aristotelean tradition (if not quite Aristotle himself) is the development of virtue, in Kant is epistemic development. Or: this is an interpretation of Kant's gloss on the second formulation, where he says of it that it is "closer to intuition" (as well as the picture of the Incarnation, though he never outright says so!), or the notion of a type of practical judgment in the second Critique and generally the place of imagination in the system (not just the metaethical but also the metaphysical framework, so far as those are otherwise differentiable here).
Now Rawls pioneered deontic constructivism, and people I think often take that phrase in a literary-studies kind of sense. However, if you've read AToJ, you can tell how much Rawls liked mathematics. So many of his descriptions (such as of mathematicians counting blades of grass for fun or range properties being for example such as "in the unit circle") and arguments depend on real appreciation for or applications of mathematical structures of a potentially quite meaningful sort. So I think Rawls meant something more like constructivism in mathematics, which is closely allied with intuitionism in mathematics. In these terms, can Kant's notion be represented not as a duty (which we ought not to have, in a way---we ought not to have made moral questions harder for us to answer) to construct particular intuitions so much as a duty to construct a specific faculty of intuition, if only in the light of the eternity of the Ultimate Good that Kant postulates for the sake of our infinite progress?