The December 15, 2008 Watchtower on page 28 states: “Our coming to know “the truth” – the entire body of Christian teachings that has become part of the Bible – and adhering to it are essential for salvation.”
WOW it actually says that? That's a pretty audacious statement even for the Watchtower.
I agree with the stance that you don't necessarily have to vocally denounce Watchtower teachings in order to be classed as an apostate in their eyes. Merely holding fast to a contrary opinion is enough to condemn you in their eyes but of course, if you don't vocalise your difference of opinion they'll never find out. However, your disagreement will eventually come out if it is serious enough, whether through your comments or your general attitude toward the leadership.
You have to remember that for the Watchtower apostacy starts "in the heart" and goes much deeper than just stating your difference of opinion. They may not be encouraged to "go on a witchhunt inquiring into personal beliefs" but it doesn't mean they don't behave like thought-police in some respects. A "witchhunt" would waste elders' time, would upset the "spirit" of the congregation andwould paint the elders in an abviously draconian light.