I'm thinking heredity has the biggest 90% influence of developing what we moderns call mental illness and environment perhaps 10% influence.
It's true that brain shrinkage is shown to be pronouncedly greater among people that are fundamentalist Christian religion, so I'm sure that a lot of brain shrinkage is going on because of listening to these absolutely boring public talks and other indoctrinating material. But that just leads to slower brain processing power, and the problems that that naturally come from aging. Having one's thinking in a box like that,, is definitely unhealthy from not giving a brain a healthy work out from time to time figuring out some problem because it's all right there in the WT publications how to handle it indoctrination. They are in the business of telling the publishers how live their life in every minute boring detail.
And so that can make some people crazy, hopeless, suicidal, and the like but not make one schizophrenic.