Why couldn't Nietzsche take the rough with the smooth, in Kant's moral philosophy?
Does the categorical imperative have a perspective from which it's reasonable, ether for Nietzsche's higher men, or the herd?
He is spidery, I might conjecture, in his recovery of transcendental judgment (after the radical breach of Hume) which amounts to a critical recuperation of the notion of a universal law that would underlie morality and act as a truth-procedure for human societies; and indeed Kant is important for the western legal tradition, and more generally maybe the institutional structure of western democracies, especially with regards to its ideas about fixed subjects endowed with transcendental or universal properties (rights, duties, etc.)
One answer is suggested in this book:
For Kofman the spider's web... [is a] metaphor for philosophical scientific and theological system-building... [as] a narcissistic illusion... [with] the pleasure of the spider's recognition of the "objectivity" of a world which it has created itself... the play of becoming has the poisonous consequence of precluding those who are entangled in this web from engaging further in creative activity... nihilistic will... from life and the sensible world of becoming toward the abstract intelligible world of static essences.
Kant's categorical imperative is similarly attacked, in the Gay Science, for the "impersonality" (Richard John White) of its imperative:
It seems that, for White, Nietzsche is concerned with individual sovereignty, not the fulfillment of our supposed rational nature (as for Kant): but the recognition that value (and here is my own guesswork) is created by and sustains our individual will.
i.e. there are no standards of judgment beside sovereignty:
the fulfillment of the individual as such.
White p42 -- Nietzsche and the problem of sovereignty