<By promoting such an intrinsically evil act he's shaking a fist at his Creator and encouraging others in evil.>
Who on earth do you think you are?
< Are you saying his desires didn't influence his theological reasoning as he searched for a way to rationalise and justify them?>
Everyone brings her or his person (thoughts, feelings, behaviors, experiences, study etc.) to her or his work; that is certainly true of theologians. However, the value of the work does not depend on those things; the work stands or falls on its own merits whether we know the personal data or not. When we do know it, that doesn't affect the value of the work, but it does give us insight into the person, and potentially into the lives of other persons who struggle in similar ways.
To assume that you can ascribe an ulterior motive to this man's work is to assume something you cannot possibly know.  In traditional Catholic moral teaching, that's called rash judgement. Get yourself to a confessional.