Some people do. It is silly and childish. However they do find some good things to speak up about once in awhile and they are least are not shy about those things. What we need though are people who will speak up about important things but have the gut so keep quiet otherwise - very few of those exist.

It is my firm belief that it isn't likely to find a the flaws in anything important (except for the obvious flaws intentionally left that other posters have mentioned) in the scope of a meeting. Once in a while you will by chance, but even if there is a flaw it needs some to look and think. People who think out loud often drive the meeting in the direction they are thinking and if there happens to be something in that direction they will find it sooner - but they miss the other directions others would have gone thinking in because they directed the thoughts of everyone.