Having a "line of retreat" -- feeling like the world won't end if they change their mind -- is part of it.
But the problem, here, is yet more general. A lot of people at my local meetup are people who I trust and like, and who accept the value of updating on evidence -- and even show respect for someone changing their minds! Even in discussions with these friends, I notice fear and loss when I lose a friendly argument. Admitting that you are wrong is a loss of status, even if only your interlocutor is watching. Every argument has aspects of status competition. I notice all this in myself, and I suspect that freely admitting when I'm wrong is one of my strongest rationalist abilities.
In others, it's pretty obvious. I can watch all this happen in their faces, when admitting that they're wrong requires an active force of will.
So, if we can find some setting for truth-seeking arguments without the status competition, we improve how quickly we learn from each other. If somehow we can remove the status competition from a discussion we're having with anybody, anywhere, then we remove significant barriers to communication.
Admitting that you are wrong is a loss of status, even if only your interlocutor is watching. Every argument has aspects of status competition.
It's a loss of status, to whom?
I've heard that expressed before, but I am usually immensely impressed by someone who can see that they are wrong and admit it, particularly if I already think they are a smarty pants. Sure, you've lost the battle, which is often just a big swinging dick contest anyway, but you've won the war. Grasping an argument and being able to see that you are wrong is much more impressive than...
Have you ever convinced a religious person to become atheistic? How did you do this? How long did it take? Were the people in some sort of life crisis, or were they just living along?
This is probably a quite difficult task of persuasion. So stories how people were successful at it could be very interesting to improve ones' persuasion abilities.
Relatedly, it might be interesting to know what religious groups have gathered on techniques to convert people to their religion - are there some manuals/techniques floating around?