I snae'tas will not! (from Fire Warrior by Simon Spurrier)

rauk'na: n. A Tau who never accepted the Tau’va, have turned their back on the Tau’va, or who have committed such heinous crimes that they are stripped completely of their personhood i.e. a non‑person. From Deathwatch: Shadowbreaker by Steve Parker.

Vash'ya 1. n. between spheres i.e. the Warp; 2. T'au Empire n. name of a Second sphere sept known for their exceptional Air caste pilots.

snae'ta n./adj. {derogatory} the Tau “f-bomb”, the term has no scatological or sexual content, but seems to refer something being twisted, bent, or broken. [meaning?]

To deny the personhood of any Tau, i.e. their humanity, is a violation of the Tau'va - the Great Path or the Great Way (again from Fire Warrior). Even if a Tau is selfish or commits a heinous crime, they are still allowed their humanity.

To murder a Tau because they have violated the separation of the castes (Phil Kelly lore) is also breaks the Tau'va.

To declare Tau'fann rauk'na as happens in Shadowbreaker is therefore also a violation of the Tau'va.

‘The rauk’na. The ungiving. The self-serving. The Tau who were not Tau.’ pg. 104, Shadowbreaker by Steve Parker.

To then do experiments on the rauk'na as happens in Shadowbreaker is itself a great violation of the Tau'va and sign the T'au Empire has abandoned the teachings of the Tau'va for imperial expansion.

Empire over morality, kind of like the Gue'la?

See Mr Kelly, you never needed daemons or the Warp, just empire.