This is the sort of situation I'd pray for when I was a JW. I loved debating scripture because I genuinely believed and (thought) I knew my stuff.
That was actually my problem - as a JW I got a bit full of myself in some respects concerning what I thought I knew. Being a "logical thinker" made me use that ability only for the good of the WT mindset. Was my own worst enemy. Took some time before I was able to step outside the bubble and truly analyse what was going on.
What did it was realising that the GB ("faithful slave") wasn't perfect, or anywhere near it (if "Christendom got things wrong, how come that made them Satanic, but when WT got things wrong, that was just imperfection and new light")...and if they were just taking a "stab in the dark" and hoping for the best in their guidance (no better than Joe Blogs publisher), why on earth was I putting stock in what they said, especially if it meant death (e.g. leaving a family motherless because she refused blood and died during childbirth)?! Why not go straight to the source, or at least weight things up myself?
It's tunnel vision, the JW will always feel their way is right....until something happens in their life that shakes them up a little bit - perhaps something really close to home that jolts them. Then and only then will they be able to take the goggles off. For your average JW, debating people is just a sport (to validate what they've already decided is true)....everything that follows this faulty mindset will only be selective "proofs" to back that up.