For sure, the witlesses are full of "mentally ill" people. They are recruiting from prisons and mental institutions, and that's where a significant part of this problem comes from. Plus, the doctrine is conducive to mental problems--just look at the "Take Refuge Refuse in Jehovah" Big Boasting Session. Everything in the world is demonized, and they are making children afraid that, unless they conform to the Filthful and Disgraceful Slavebugger in everything, they will die "any time now".
Some symptoms: Depression not associated with specific losses. This is caused by deprivation from the religion itself. The witlesses have little or nothing to look forward to. They celebrate nothing, aside their REJECT Jesus Party and the a$$emblies. Crap jobs are preached--anyone with a good job is "materialistic". They just about ban entertainment, so the boasting sessions become the "brightest" spot in their lives by default.
And, what about the pedophiles within the congregations? And, I would say that a fair percentage of those pedophiles do it because they get their kicks out of ruining children's lives. Anyone that actually gets their kicks out of ruining others' lives is "mentally ill or impaired"--and that's the "nice" term. (The not-nice term is "scumbags, slimeballs, and pigs", and these people deserve those labels.) Not to mention the ones that kill their children because they cannot find a damn coat quickly enough, kidnap worldly children and enslave the resulting children, and even the one witless that was busted in July 2009 after killing and eating a baby! I don't know of any mentally sound person, not in a dire emergency situation, that would stoop to killing and eating a baby.