Seriously, their society sounds so overtly positive in the face of a preposterously hopeless and uncaring universe, there’s no way even the codex is telling the truth.
It’s like being stuck in a malfunctioning elevator with the Adoring Fan from Oblivion, or trapped in a burning home with Ned Flanders; the overt positivity just seems like it’s projection and there is a hidden darkness element somewhere waiting to come out.
The “Greater Good” religion simply sounds too good to be true. So they should all be destroyed, and their societies wiped from existence.
Edit: it looks like many people here don’t understand the obvious hypocritical irony and sarcasm written here…
I mean, it depends on which version of the lore you take. Their culture is repressive, with less social mobility than the Imperium or the Eldar, thanks to the caste system. The Ethereal Caste are doing something hinky and mind-controlling to everyone else. The one General who said “hey maybe we should learn how to fight up close occasionally” was banished. There’s a lot of darkness there, and the disconnect between the Tau and the Warp makes those “little” things more notable.
Imagine if the Tau get eaten by the Tyranids or a Genestealer Cult. They might not cast the Shadow in the Warp, removing the one form of warning of their presence.
If I remember my reading they discovered the cult on one of their colony worlds. Then they developed a cure and got on with life.
There may have been some “you will have the injection for the greater good” involved but quite frankly I’m fine with that.
I mean, getting a needle vs. turning into a Genestealer vs. a pulse carbine in the head? I’m not a fan of injections, but I would take that one!
Less social mobility than the people with hereditary nobility? It’s not great, but the IoM are pretty poor at it. I suspect you misunderstand the T’au caste system; admittedly it probably shouldn’t be called that as it doesn’t really function like a real world caste system.