Changing Minds in Opposite Directions
John Brockman has collected answers to the question: What have you changed your mind about? It seems obvious that someone would only change his/her mind because of very strong evidence so people changing their minds in a given direction would show the opinion must be the case.
There are also the cases of Douglas Rushkoff and Lee M. Silver who changed their minds about whether others would agree with them. They look like they need an excuse to avoid changing their minds in more important ways.