Do people have a tendency to stick to one opinion after they formed it? Scytale's assessment, from the science fiction novel "Dune Messiah" (1969)


  When a creature has developed into one thing, he will choose death
  rather than change into his opposite.


While reading some discussions on Meta Stack Overflow, it dawned on me that it might not be the best format to start constructive discussions. Once people pick sides in a discussion, they have a very high tendency to stop approaching the discussion from the other angle. People will dislike certain parts of a proposal, and then become vehemently against the entire thing, instead of trying to participate in resolving the issues they raise.

Is this an established psychological phenomenon?
Yes.  But why should it be so?  One can approach the question from a number of directions. For instance, Cass Sunstein talks about how information cascades can create the path-dependent effects you describe: person A says something, which steers person B toward the same opinion, with the result that group decision-making heavily overvalues inputs of early responders.  (James Surowiecki also did an excellent popular science treatment of this topic.)

So much for the hobgoblin of little minds for groups.  Within the individual, the topic has been addressed through the dissonance literature, in which cogitation contrary to an established position carries unpleasant consequences, both hedonic and adaptive.  Particularly, maintaining a consistent set of mental beliefs seems to be important for efficient action selection, possibly as a consequence of the way semantic information (including motor control programs) is represented in the brain.

The result of all this is that, as you suggest, people establish a position, and then are motivated to keep it, which is not news.  What is surprising is that this annoying behavior is probably highly adaptive and a consequence of our neural architecture for knowledge representation and decision-making.  In other words, a feature and not a bug.