What is even more entertaining is that when they do know people from the other group, they have a habit of treating them as shining exceptions to the rule, not questioning whether or not the rule is even valid.
That doesn't stop with the -ism's, I routinely run into programmers learning about DRY and cargo-culting the hell out of it. People seize onto absolute rules and superficiality, failing to consider deeper conceptual dissimilarities that would negate the application of the rule.
Yes, you can interpret it so it makes sense.
No, that sensible interpretation isn't the one that caught on.
It has a nasty symbiotic relationship with the "But you're one of the good ones" phenomenon, which is what you're more directly referring to.