If you and a fellow Jehovah's Witness went to a house where the homeowner brought up a Watchtower doctrine which you secretly disagree with, would you defend it or tell them what it is you really believe?
Either way you are at a loss.
Defending something you disagree with is living a lie and telling a lie.
Not defending it and telling the home owner what you really believe makes you an apostate by Watchtower Society standards.
That's a pretty difficult situation to be in since you have another Jehovah's Witness with you who would probably stab you in the back and report back to base.