Please let me know whether you detect objectionable points in my attempt at reconstructing Kant's universalization principle.
Reference : Groundwork of the Metaphysics of Morals.
(1) Free will does not act in an heteronomous way.
(2) Free will is autonomous, free will is to itself its own law.
(3) The only law a free will obeys is " be yourself", " let your own essence be your law"
(4) Will is by definition a rational appetite, a rational desire ( for will is the superior faculty of desiring).
(5) A rational appetite acts upon universal rules ( for reason in the faculty of the universal) . ( It would not be rational to claim " I am entitled to do this action because being myself gives me special rights". Acting rationally implies that I recognize I am allowed to do action A iff for all person x , if such and such conditions are fullfilled, x is allowed to do action A)
(6) The only law a free will obeys is " act upon universal rules" .
(7) Acting upon universal rules implies not attributing privileges to oneself, and hence, being " just", " moral".
(8) A free will is a moral will.
(9) Being moral is equivalent to acting upon universal rules, or rules that are able to stand the test of universalization.