Tom Jacobs has an excellent piece at Pacific Standard, Threaten My Group, and I’ll Belittle Your Science. He writes:
Newly published research provides at least a partial answer. It finds scientific findings that challenge the assumptions of a group you strongly identify with motivate people to derogate the research in online comments.
When informal membership in a group—say, the anti-vaccine movement, or those opposed to genetically modified foods—informs your sense of self, and/or provides a feeling of pride and belonging, a perceived attack on its basic beliefs is grounds for a counterattack. Today, that often means writing nasty, dismissive comments online. ...
... While conceding that there are a number of reasons why gamers would choose to angrily argue with the science rather than seriously consider its implications, the researchers focus on one particularly interesting psychological framework: Social identity theory.
This school of thought contends that group membership (be it political, religious, or something as innocuous as being a fan of a particular sports team) is a significant source of our self-esteem. It follows logically that members have an interest in boosting the group’s status (and degrading the status of competing groups), since its prominence, or lack thereof, rubs off on ourselves. ...
... Perhaps this discovery can provide an opening for educators and policymakers as they attempt to get around this frustrating psychological block. If scientific findings are to be accepted and acted upon, they have to somehow be presented in a way that does not trigger a defensive reaction.
We remain, in many ways, a tribal species, and if you challenge my “tribe,” don’t be surprised if the response is a metaphorical poke in the eye.
To this I would add that the reason a great majority of people hold a scientifically sanctioned position is not because of science, but also because of social identity. Science affirms my narrative and my tribe. "Science" becomes a weapon to deploy against other tribes. It lets me beat my chest in defiant superiority. It becomes a club with which to bludgeon those who threaten my tribe. Advocacy of the "scientific" position frequently has precious little to do with a concern for science. I don't care if it is climate change, vaccinations, evolution, GMOs, nuclear safety, or a host of other topics. It is far more about affirmation than information.
I'll also add this - if you think you are not affected by this dynamic, then you are likely either Commander Data from Star Trek or delusional. ;-) It is inescapable. We are communal creatures and tribalism is always a factor. The realistic response is to continually strive to be self-aware of our own tribal issues and be more accepting of the tribal buttons we push in others. Only then can we move toward genuine dialog.