What specific diagnosis are you referring to in regards to the brainwashing comment?
"Mentally ill" is a broad category of hundreds if specific medical conditions.
What is your source material for the statement that brainwashing=mental illness?
Let's start there so we can understand where you're coming from.
mentally ill, the links go on to show most religious people are
I'm sorry but those links do not provide evidence.
As we've discussed, many of the things people typically consider mental illnesses ("Axis I" disorders) are brain conditions. Many brain conditions, not just one. To prove that most religious people are mentally ill, we'd need evidence of diagnoses for 51% of a statistically significant sample of religious people.
And then, not sure where you're going with this, but correlation does not prove causation. So imagining said proof existed, we'd need to eliminate other reasons for correlation.
I remember reading some article once about MI and JW. Might have been on pew.org or something like that--maybe you can find that since you're interested in the topic. I don't know if it was evidence though--IIRC it was more of a general anonymous survey that had to be taken with a grain of salt.