Well, to be fair it’s the one gaining the most traction, arising through need, from the Hindu meaning from which it originated.
Flowers’ treatise on the subject covers it in depth - that “light” and “dark” are both simply tools for ascent. That may include a leaning towards dark where needed as the prevailing culture and spiritual bonds are “light” in concept.
Unity by its nature means no dissent, though, no disunity, so how do you attain this without prioritising and favouring, however covertly or unwittingly, those who agree, and disfavouring those who disagree?
I can’t find the link now, but a few years ago I read a statistical analysis that showed people on the TV show “The Weakest Link” were prone to be voted out, not based on their performance (which would be the rational choice, maximising the eventual prize) but based on where they stood - if a small group remained on one “wing” of the semi-circular podium, they would disproportionately and irrationally vote against individuals opposite them, even where those individuals were answering correctly.
“Us against them” is such an innate survival drive, since it did confer benefits for most of our existence, that simple rules and procedures within any group are unlikely to prevent it.
Create your unity, and anyone who disagrees will become “them” - you can have all the fine speech in the world, but so far no group of humans unifying behind a “truth” that they believe is superior has failed to begin silencing, and occasionally eliminating, the people who disagree.
Groups who fail to do this, furthermore, usually end up on the sharp end of some more motivated and more commited group who are willing to do the dirty in the name of their One Unifying Truth.
I find it better to work with human nature as it is, playing to its strengths, and then allow evolution to occur as it will, than to hope this time things will be different. 
I’ll get back on this later, need to EAT! 
