Agreed if they're prepared to go door to door and set up stalls to dispense their teachings, then they need to be prepared to defend it. Nobody should be allowed to spew out lies that affect millions of peoples lives, innocent children who have no say and not be challenged.
I think pointing out the organization history is powerful, this lead me here and the rest was history. If done in a respectful way, it will leave a empty feeling "doubt" that needs to be looked into. Eventually when they realize the bOrg doesn't touch on the subject and if there honestly seeking answers they will go online. If they're content in letting someone else think for them, well they're home. The preaching work nowadays is nothing like it was in previous years where discussion and debate was welcomed, preparation was necessary. Now you just see them sitting next to a cart and making no attempt to reach out to people they are just counting time.