Do they not elsewhere require members to agree with the whole range of Watchtower doctrine, including interpretations (of the Bible) that are "unique to Jehovah's Witnesses"?!?
For instance, I wholeheartedly endorse the apostolic decree in Acts 15. It was appropriate that newly-converted gentiles try not to stumble their fellow Christians who were Jewish by eating meat from idol temples or from animals killed by strangulation, drinking blood, or fornicating. In this of course I heartily agree with the Watchtower interpretation - in C.T. Russell's time.
Try this, active JW's: Read another interpretive Bible than the NWT, such as the New Living. Because today, as you read the NWT or a Bible that is doctrinally neutral (and trust me, the NWT is not), you add meaning to each scripture as you read it because you have heard it before. The NWT goes along with the meaning you add, and the neutral text does little to work against your current understanding.
Ah, but read a Bible written by people with different doctrines who, like the NWT translators, alter word choice to fit their beliefs, and you will find yourself reading a whole different book. You'll find yourself questioning the translators' choices, challenging their beliefs. And, finally, the omen of free thought, you'll find your own comfortable beliefs challenged.
The fact that the Watchtower makes this boast only indicates that they believe their followers are fully programmed to believe they are free, and that even those who fancy themselves just a little rebellious - but in a good, Laodicean way - will only repeat in their minds what they have already been taught when verifying things in the Bible. (Good thing for the WTS that Galatians comes so late).
Yes, they believe taht they are free, and are often told so. This is the most insidious form of imprisonment.