Someone who held a highly visible calling in my stake and is seen by everyone as a rock solid believer (and who is, in every way that is important) made the following statement in response to a discussion being held in the stake center chapel between stake leadership meetings:
"I really hate it when members say, 'I know this is the only true church on the face of the earth.'"
He went on to say that he believes passionately in the Restoration of the Gospel and the Priesthood, but he is concerned that non-members and members alike will interpret that statement to mean that we believe there is no truth in other religions.
My point in sharing this experience is that this was a very visible leader (who has had some astounding spiritual experiences in his life) saying something that others who might have heard it without the follow-up explanation would interpret as critical of the Church - while many of the non-leadership members who weren't there would never guess he feels that way.
That is a long-winded way of saying that I have no idea how many of the people in my ward and stake are "extremists" (take an "all or nothing approach" to the LDS Church and the Restored Gospel) and how many are not, since those aren't things we generally discuss as topics in and of themselves. I'm fine with not having that discussion generally, since I don't want to shake anyone who is happy in their own paradigm - but literally hundreds of similar experiences in my life make me believe fewer members are extremists than perhaps most people (including many members) assume.