I believe they are sincere.
However, sincerity isn't enough a redeeming quality when they're sincere about a myth. The myth that there's such thing as one God's visible organization on earth. And that they've been chosen to lead it. Sure, they love the adulation and power trip.
They're aware of the cracks in their cosmos; yet the alternative to their belief system is the complete dismantelling of their authoritarian system, and therefore they simply cannot afford that. This is where they're inexcusable. If they were truly humble men, they ought to consider the possibility that they aren't the chosen ones, nor Jehovah's Witnesses are special among other Christians. But they simply don't, because they've created an idol- the organization - and now they must keep on worshipping that idol. Like the israelites near Sinai, they made a golden calf and call it "their God that took them out of Egypt Babylon The Great", i.e. the image of the living God Yahweh. Only that image is a de facto replacement of God.
Picking what Prologos said, they are like the pathetic prophets of Baal: "Oh Baal, answer us!"...but there's no viable answer. So they do and say all kinds of absurdities hoping that eventually they get the right charm to get their confirmation / vindication, that is, Armageddon. In the meantime, they play "follow the leader" with 8 million people.
They are sincere. But they are deluded. And there's no greater danger than a sincerely deluded person, x 8.
Eden