Great post.  I find a lot of leaders lack the courage to initiate or invite this kind of conflict, and I am often coaching them to consider ways in which they can invite it.  One of the most successful in my experience is, ironically, to delegate it.  Let someone else play the role of dissenter, devil's advocate, even curmudgeon, but be specific about that role to the rest of the team so it is valued.  What ideas have proved successful in your work with leaders to avoid this issue?