Thinking is a social activity

 No individual alone, exclusively, can have the one and only right idea. Justice Holmes was expressing the pragmatic view,* in spite of himself. 

"He thought James had made scientific uncertainty an excuse for believing in the existence of a unseen world." 

         ...

"We do not (on Holmes's reasoning) permit the free expression of ideas because some individual may have the right one. No individual alone can have the right one. We permit free expression because we need the resources of the whole group to get us the ideas we need. Thinking is a social activity. I tolerate your thought because it is part of my thought—even when my thought defines itself in opposition to yours." --The Metaphysical Club: A Story of Ideas in America by Louis Menand 

* "Hands off: neither the whole of truth nor the whole of good is revealed to any single observer, although each observer gains a partial superiority of insight from the peculiar position in which he stands." WJ, On a Certain Blindness in Human Beings