Each side in a controversy feels a need to offer bias theories to explain why the other side disagrees. Without such bias theories, observers will wonder why they should side with one side against the other, if both sides have reasonable people with good reasons for their positions.
The problem is that we are not critical enough about these bias theories.
An example of a "bias story" would be to say, "X's research findings are suspect, because X receives funding from Y." Hanson's notion of a bias story is related to my concept of a Type M argument.
I simply cannot say enough good things about the Overcoming Bias blog. Consider this post by Jason Weeden.
Research from psychology and neuroscience shows that your brain has organizational characteristics similar to this caricature of the Bush Administration. There are systems that are responsible for powerful, simple emotional reactions that serve to focus other systems to give fine-tuned attention to your brain's priorities and preferred outcomes. Most of the detailed systems don't care much about why they have the jobs they are given; they just do the work of carrying them out in a highly distributed, bureaucratic way. And you -- the conscious, chatty you -- are that dimwitted patsy, the misinformed press agent. The conscious you is not the President and you're certainly not Karl Rove. You are the Scott McClellan for your bureaucratic brain. You're constantly being duped into believing public-friendly stories about yourself, because your entire job is to tell stories handed to you by ruthless, clever, unconscious communications systems. You're not the whole head; you're just the talking head.
You can't even trust your own introspection, because your press agent simply doesn't have direct access to the Oval Office.