"Although mental illness is not something so static and contained, and rather has a constellation of elements, at its core is the idea that one’s experience of the world is at odds with society’s expectations of that experience (and that world). Those of us who suffer live with this struggle intimately know the physical and emotional affects of that dissonance.
By contrast, white supremacy and the agents who act on its behalf do not experience dissonance. They are rational actors engaging in rational action within a legitimate system of domination. There is no divergence between individual behavior and societal expectation. They are mutually reinforcing.
Calling white supremacy a mental illness is complete and utter definitional nonsense.
The shooters and associated ideologues do not experience any dissonance, they experience a disconnect from reality.
For all intents and purposes, the shooters are dominant in all the ways they expect: socially, sexually, economically, and politically and the world reaffirms that for them over and over throughout their lives. Fearing that that dominance is under attack does not qualify as a mental illness any more than your average Trump supporter’s beliefs qualifies as one.
If you’re experiencing a failure of social intelligence, does that make you mentally ill? That would mean that children were mostly all mentally ill, and that any especially gullible adults were mentally ill, as opposed to simply harboring hate in their hearts or not being bright enough to parse political information."
I would also point out that mental illness, though portrayed in the media to be associated with violent outbursts, is statistically correlated with being much less likely to harm others and much greater likelyhood of experiencing harm by others.