We can argue about this all day, but the crux of the issue really is what the Watchtower is doing via this association. The level of involvement can vary once you gain NGO membership.
I sincerely don't buy into the "using the library" excuse. The Org has a history of pushing it's freedom to preach agenda using legal means,
and what seems more logical to me is that they have been and continue to influence decision makers who hold weight in extending "the work" to countries where this is prohibited.
I can even see how they probably reason this internally. At a high level, the leadership justifies this by a "means to an end" excuse, where yes they are dealing with the "harlot" but with the intention of expanding Jehovah's work.