I look at it the other way: right-wing conspiracy theories pander to textbook mental illness. They’re more susceptible to such bullshit and thus it’s like a magnet that attracts these deranged individuals.
One way or another I am personally convinced a large chunk of dyed-in-the-wool Trump supporters are not of mentally sound mind.
Drugs, head injuries, lead exposure, etc. You look at the average attendee of a Trump rally and they do not look physically healthy from the outset.