You can never "win" the discussion. The CO is a devout JW and will not see nor accept any serious accusation against the organisation. He will likely accept that the people are imperfect, even those in the gb. etc but that there is only one organisation to acquire salvation. And then he will surely ask: Or do you think salvation can be found outside Jehovah's organisation" .I recommend not even start the discussion to prove they are wrong and you are right.
I would say: who died for me? Jesus. Who should I put faith in for eternal life? Jesus. Who is my judge? Jesus. Hence, who should I follow or obey Jesus.
Bye CO.