What's wrong with the JW religion...(as brief as this can be!)
Historically humanity has gone through different stages of development. To grossly oversimplify this and keep it relevant to the JW, there is the basic group phase whereby individuals realise that working together ensures better survival and quality of life. It starts from the family and extends out towards tribes etc. This developed into hierarchy structures etc with their laws and codes for self preservation as a society.
The next (overlapping) phase that we're still going through (as evidenced by war/racism) is one of accepting people from the "outside groups". Accepting people of different nationalities, races, sex etc. Whether you believe in evolution or not, accepting this progression of civilization is vital for long term survival, and those who don't submit to the progressive flow will not bode well either individually or as a whole.
How does this tie in with the JWs? This religion is stuck in the old mindset of "us vs them" (the ancient priestly hierarchical rule of nationalism). No matter which way you dress this up (e.g. the rich vs poor, virtuous vs savage) it's the same crap that won't last...it'll die out with each subsequent generation, much like sexism has done over the decades.
There's only so long you can keep a person back; trying to delude people into a superiority complex (ultimately "us vs them") only works so long. People start to small the BS and wake up. Ask many ex JWs about this and it'll be high on the list of things that made them uncomfortable as a JW (made to feel as if everyone else was "unclean" except themselves).
Actually this should be called "spiritually" because that's where the real problem lies (theology changes throughout history, but spirituality remains pretty constant). Watchtower is a pretty cold corporation that's devoid of spirit. By spirit I mean a person's better inward drive towards what they currently believe is true/pure/good. The WT takes this freedom away from the adherent, and that's a huge thing - i.e. your free will (the main thing that makes humans "special"). Spoon feeding anyone into a state of drifting through life (dependency) is the worst thing you can do to them, and that's what WT does. Many can't quite pinpoint this error in the WT but they know it just doesn't sit right with them deep down, and many leave as a result.
In a nutshell:
1) Backwards and unethical philosophy to social structure - "us vs them"
2) Enslavement of a persons spirit (whatever you define that to be) - "we'll tell you exactly how to feel/think"