I find it helps to clarify things for a JW who is making all sorts of excuses for the Society's voluntary association with and service to the UN by interrupting and insisting that they stick to the Watchtower's teaching on this matter while discussing it.
Have them first read Revelation 13 and 14 regarding the mark of the Beast and penalty for receiving it. Remind them the Society teaches that the UN is the Beast, a Satanic enemy of God, and then, without any further commentary, ask them to proceed with or repeat their excuses while making an adjustment of just ONE WORD: which is, to be scripturally accurate and always refer to the UN as "The Beast", as the Society has identified it.
See how far they get before they go bright red or can't continue.
If they won't do it, ask why not, is it the Beast or is it not? If there is nothing to be ashamed of, then why is employing such Scriptural accuracy a problem?
Even the most blind and dismissive JW can find sudden clarity as they feel the creeping horror of blasphemy while saying things like "We only associated with the Beast to be able to do the preaching work better." (to function - "to buy and sell" Rev 13:17-18)
What a lot of power in just one word.