Do you think your organisation is perfect?
No
So what’s wrong with it?
That's pretty good, but it just sets up the line "It's run by imperfect men".
And if you press them for specifics, they'll just chirp on about "new light" and "old light" and how the "old light was wrong" and so, ipso facto, the imperfect men back then got it wrong, and maybe there will be "new light" in the future, yadda yadda yadda.
IMHO, a better approach might be "Is there anything the organization could do, or teach, that would convince you that they are not God's chosen ones?"
If they say "no", well, they are hopeless. Move along.
If they say "yes", ask what it is. Odds are the organization has done or is doing something like that already.
E.g., political involvement? UN NGO-DPI membership 1991 - 2001. Child abuse coverup? Too many examples to mention. Hypocrisy / double standards? The elders manual book about how elders can "get away" with past sins that a "regular" JW would pay for. Printing falsehoods? The dozens of out-of-context quotes in the Creation book, Trinity brochure, etc. And so on.