Unfortunately, I cannot look at the actual post and am merely trying to infer its contents based on posts on LessWrong. The only major argument I can make in favor of using the word "tribalism" is that the term has useful negative connotations:
"This is tribalist thinking." == "This is silly, savage thinking which we are trying to overcome as rationalists."
Various people (including Konkvistador who has been talking about it the most) have launched their blog More Right
"A group blog, More Right is a place to discuss the many things that are touched by politics that we prefer wouldn’t be, as well as right wing ideas in general. It grew out of the correspondences among like minded people in late 2012, who first began their journey studying the findings of modern cognitive science on the failings of human reasoning and ended it reading serious 19th century gentlemen denouncing democracy. Surveying modernity, we found cracks in its façade. Findings and seemingly correct ideas, carefully bolted down and hidden, met with disapproving stares and inarticulate denunciation when unearthed. This only whetted our appetites. Proceeding from the surface to the foundations, we found them lacking. This is reflected in the spirit of the site."