Those grey areas are carefully retained so that everyone, especially the powers that be, have some venue of demonstrating the superiority of their balancing act between Wise and Reasonable. (Which is the dichotomy/continuum of Spiritual-Physical.) Such postures are actually bids at imitating God's ability to be multiple dichotomies, in particular the Just-Merciful and Love-Hate. So, there are ideals we cling to, ie, "It is best to be wise, it is best to be spiritual, it is best to be just, it is best to be loving". But there are realities that we must deal with upon this mortal coil, so that "It is sometimes necessary to be reasonable, to be physical, to be merciful, to hate".
Any time there is a grey area, it is for the purpose of the practitioners of this craft of balance to impersonate God with his imperceptible, inscrutable, inconceivable gradients of finely (impossibly) incremented standards. Ie, they can be recognized and adulated for having a truly dizzying intellect, as it were a truly dizzying sense of conscience and freedom of speech, while not being required to give reasons. It this way they get to be god for a moment by giving arbitrary rulings and not being held accountable.
Even if Paul said a bit of wine was ok, the WTS could easily make it as unscriptural as they did for smoking which isnt mentioned, if they wanted to. It serves them, however, to maintain an edifice of genteel civility in at least a handful of things, lest too much black and white in simplicities betrayed their utter disregard for Actual, Real, Native conscience.
They desire a "Bible-trained conscience" in their rank-n-file, one that can be trusted to respond with stupefied awe to the inscrutable rulings of conscience by their superiors. Rank-n-swiss who question the motivation, standard, meaning or conditions behind the formulation of the local deity's particular ruling on the conscience matter do not have a "Bible-trained conscience".