Do think that religious organizations like the WTS and any other that exhibit cultish characteristics should be exempt under current tax law? Given that most citizens in democratic nations support these exemptions due to fact that most mainstream denominations support their local communities through charitable activities, I find it reasonable that groups who do not support anyone outside their organization should not be exempt.
It's just...where do you start? If you select one group to start with, e.g. the Watchtower Society, they will claim that they're being picked on for unfavorable treatment and may gain sympathy from a disinterested public.
People here in the USA will stand up for freedom of religion, even if they don't know that a group is secretly profitable but presenting itself as a "non-profit religion".
But I think what has happened to the WT Society in France (getting assessed back taxes) proves the reasonableness of your point. Maybe other governments will follow suit at some point.
I believe that every religion, regardless of its affiliations or lack of them, should be taxed and and licensed. They are after all, far more dangerous to the health of human race than cars, doctors and farmyard animals, all of whom require a license.