"The point of THIS thread is to point out that Ayn Rand, despite her avowed hatred of Kant, believed something about the nature of moral failure very similar to him, namely that particular transgressions don't occur on their own but must be derived from a general one involving a perversion of our attitude towards reason."
Yes, God is to Kant what Reason is to Rand: a metaphysical [transendental] font.
In other words, ultimately we must evaluate and judge human behavior based on an assessment of Right and Wrong that transcends the existential reality of ambiguity and uncertainty...of contingency, chance and change.
As soon as you bring Kant and Rand down to earth, they are lost without their Words. Without their assumptions about What Words Mean.
"I don't know what 'can be attached to dutiful behavior' means. Do you mean that we have (A) a set of attitudes towards various actions as well as that (

there is a set of real duties, but that (A) and (

only overlap if (C) God exists? And where does this question of what ought to be enforced come in?"
Well, let's bring this down to earth.
Kant and Rand both seem convinced we are "obligated" to comport ourselves in one way rather than another. It is our "duty" to behave morally rather than immorally. Why?
Obligation and duty are different from suggestions that rules of behavior are necessary in order to facilitate more rather than less functional social, political and economic relationships. Making that distinction is basically my aim here.
Behavioral rules are not the same as obligations---except in the broadest sense that human interaction inherently requires a set of rules to ward off chaos. Or to obviate the brute facticity embedded in a primitive survival of the fittest mentality.
If Kant and Rand were participating in this exchange I would draw them into a discussion of moral hazard as it relates to the real world. How far would their arguments go in circumstantial contexts that complex, convoluted and contradictory?
Perhaps someone here shares the philosophy of either Kant or Rand. Perhaps together we can choose a particular moral quandary and discuss these concepts more...existentially.
the nihilist