Unfortunately, the problem of due process is inherent in all religions, not just fundamentalist ones like Jehovah's Witnesses. Terry's "invisible gun" is not only held by the Society, but by almost every God since the concept's advent.
For example, Yahweh puts the invisible gun to heads of all Christians with the threat of Armageddon. When it comes (teehee!), if you haven't been doing what he says, you're toast. Probably eternally burning toast too. That aspect of the theology removes the possibility of free will. God says "My way or I'll kill you. Maybe not today, but I'm definitely gonna get you."
As Narkissos noted, due process arose in human institutions out of a power struggle, recognizing that every human can err in judging fairness. In religions, God holds the power, so no struggle, no recognition that God's rules might be unfair, or unfairly applied, thus no due process. His instruments do his work, and if you don't like it, well you certainly can leave the religion--unless you lived in the Middle Ages, where they'd burn you at the stake.. :(
A religious organization that isn't directly controlled by God cannot, by its very nature, be fair. The self-evident lack of any fair religion simply increases the already overwhelming probability that God just isn't there to make sure things are being done right.
A great topic Terry!