I am not saying all JW congregants are pessimistic, but I would go as far to say all PIMI JW congregants are pessimistic.
Why do I say this, my wife is my measuring stick. she has barely an optimistic bone in her being. She will only focus on the bad parts of anything. I have missed out on so many opportunities in our life together due to her pessimistic personality. I am partly to blame because I have never wanted to rock the boat and always keep her feeling in mind. I can't say the same for her when it comes to her keeping my feeling in mind. but I can't speak for her.
But, This is the goal of cults like the JW's. Keep the congregants down with a bleak outlook on life. In fact I would go as far to say all religions do this. Because in reality I believe all religions are cults to varying degrees. The JW cult being one of the worst.