These are good points. The middle of my examples (the one I thought had problems but wasn't a total fail) was trying to do a mix of joint prayer (warning bells should sound there) and exposure to different perspectives (informal education). The first and third both have the goal of education (not evangelism), and one works way better than the other.

I think you're right that the key is whether you're there to share perspectives or to share The Truth. As dvarin notes, if you "know" something is "the truth" then why would you agree to relativize it, to couch it in terms of "we believe" instead of "this ist rue"? But that is exactly what kills the dialogue, because you're asserting your truth over all the other truths in the room, and everybody else has the choice of either arguing with you or disengaging. So, knowing that people have deeply-held beliefs, how do we nonetheless get them to modify how they interact with others, in the interests of having a discussion at all? That's the challenge.