I would say that the important thing is more humility of presentation than humility of willingness to speak at all.

I agree, it's OK to ask what you think could be a stupid question. It's better than not asking, as you lose a chance to learn. It's not OK to insist that you are right and she is wrong once an explanation has been given, even if it does not make sense to you. Though, given the usual inferential distance problems, it's perfectly fine to ask for clarification.

From my experience, I think that your estimate of the odds of encountering a comment "which blows apart their argument" as about 1% is overly optimistic. Maybe in some other fields it's different. At best you can expect a minor correction or a qualification. If the expert is any good, they probably have heard it all before, and if they aren't, their ego would likely prevent them from admitting that they are wrong, anyway.