https://en.wikipedia.org/wiki/Ingroups_and_outgroups
"In sociology and social psychology, an ingroup is a social group to which a person psychologically identifies as being a member. By contrast, an outgroup is a social group with which an individual does not identify."
https://en.wikipedia.org/wiki/Social_identity_theory
"A social identity is the portion of an individual's self-concept derived from perceived membership in a relevant social group.[1] As originally formulated by Henri Tajfel and John Turner in the 1970s and the 1980s,[2] social identity theory introduced the concept of a social identity as a way in which to explain intergroup behaviour.[3][4][5]"
Still, individuals do change their ingroup membership and can remain as intolerant to then fully new outgroup. It would be good to have a name for this phenomenon: being intolerant to whatever person's current outgroup is. And there is one, which happens to have more uses than only this:
https://en.wikipedia.org/wiki/Prejudice
"The word is often used to refer to preconceived, usually unfavorable, judgments toward people or a person because of gender, political opinion, social class, age, disability, religion, sexuality, race/ethnicity, language, nationality, or other personal characteristics. In this case, it refers to a positive or negative evaluation of another person based on their perceived group membership.[1]"
You have just described at least half of the dozens of posts on that blog.
(There's a best-of list, still intimidatingly long, here: http://lesswrong.com/r/discussion/lw/mmg/yvains_most_importa... and a best-of-best-of subset of that, unfortunately with only the titles and no links, here: http://lesswrong.com/r/discussion/lw/mmg/yvains_most_importa.... I haven't looked through either of those lists and make no claim that they have successfully selected the best. The lists include not only posts on Slate Star Codex, but also others -- mostly earlier -- from the same author elsewhere.)
This is something I've never seen stated outright before, and it seems totally true to me.
(For the avoidance of doubt, my comment that what you said applies to lots of things on SSC wasn't intended as any sort of criticism -- I wasn't saying "boo, you failed to describe the article in a way that distinguishes it from the others" but "yay, SSC has a lot of really good articles".)
There's a really amazing post here about outgroups and the distorted way we reason --- or fail to reason --- about them. It's a bit long, but totally worth the read.
http://slatestarcodex.com/2014/09/30/i-can-tolerate-anything...