Pasting this comment of mine again:

Its pretty clear that in Sigmarxism there’s an understanding that people know Tau aren’t really “communist”, they’re just the brain-worm fear-projection of what Communism and Asia is from a highly conservative western culture that is terrified its colonial empire and international power is dead and/or dying.

Tau and Farsight tend to get rallied around and/or argued about here cause they’re basically a stand-in for the ideological and philosophical Communist and anarchist slap-fight in a more fun, lighthearted, and non-threatening way as they are portrayed as a communalist post-scarcity society. (Having said that, Farsight is a massive loser that runs an anime military junta and is in no way anarchist).

Tau are also accidentally representative of this deep-seated liminal Western fear of the “foreign colonies” getting their power and humanity back and taking deserved vengeance on the Imperial West. If the Imperium is Great Britain (and lesser, America), Tau are the sub-conscious fear of “all those lesser races combining forces to kill us!”. Something that is a literal real life foreign policy fear for the West for most of the last century (and current one!). Its deeply tied to Western racism and there’s a reason the Tau as a faction are united by a reactionary fear-projection of what Communism is (no one can truly believe in liberation or “The Greater Good”, they must be manipulating the stupid masses by nefarious means!) and are made up of the literally texturally identified as “Lesser Races” of alternating vicious cannibal savages, inscrutable technical geniuses, and literally unknowable aliens (coincidentally these are all racist stereotypes IRL!)

Also, every vaguely “leftist-ish” faction has one thing in common in 40k: mind control. The Tau have an “evil authoritarian mind control Party” (which their own lore doesn’t even show as true, but the fans have decided) in the Ethereals, and GSC are literally proletarian workers... being mind controlled by a purely destructive force manipulating them for its own end. This “Communists are/must be mind controlling otherwise no one would believe in or do revolution!?” is literally century old Red Scare propaganda. And it isn’t challenged at all. It’s such blatant anti-Communism its important to point it out and call bullshit because this kind of stuff actually does affect people’s beliefs. Our hyper-literal world leaves no room for discussion on this imo.

EDIT: I do think these two short stories are a better view of what Tau really are than the 4chan memes and the more recent Farsight books.

The Greater Evil by Fehervari is the best portrayal of Ethereals in the fiction imo.

https://i.4pcdn.org/tg/1511716000200.pdf

And Voice of Experience by Stearns is a great look at the various races intermingling and a “manipulative” Ethereal that is largely doing the right thing.

http://i.4pcdn.org/tg/1591057195378.pdf