I had honestly never run into this brand of nuttery until a couple days ago via a youtube post.
Hypothesis: There is no such thing as mental illness.
Now, I'd heard anti-psychiatry arguments, usually from Scientologists who are nakedly trying to sell their own brand of psychotherapy, and people who bring up the horrific history of psychiatry from lobotomy to electroshock therapy (these things can't be readily denied) but I had never heard anyone suggest that mental illness is, like, not a thing man. Especially in the face of modern neuroscience.
I guess having a girlfriend for over a decade with chronic, clinical depression caused by *gasp* neurotransmitter imbalance put me in a bubble of people actually affected by, and thus unable to blanket deny, mental illness.