Dr.Who,
I left because I started changing and growing as a person and started to see some of the hypocrisy and lack of love in the congregations, especially as I was married to a disfellowshipped person (they practice shunning of former members). I was basically treated as somewhat tainted myself, so I was very loney. I also was in a very bad marriage that I was not allowed to leave even though he was disellowshipped (they only allow divorce on the grounds of adultery). Basically, I just could not do it anymore. My physical and mental health began to suffer and I came to the point that I just didn't see how any lovinng God could possibly want me to live like that, and if he was not a loving God, then why was I suffering for him? I left and have never been happier.
I was still so brainwashed that I thought they were closer to what the bible taught than other religions, but I just didn't care anymore. Since then I have learned how very wrong they are on many things, and how they manipulate the scriptures to justify their beliefs and how they hide their history of doctrine changes, bad date predictions and flip flops. It's not hard to prove they are wrong to any objective person, it's just that they use mind control to keep people from questioning their belief, so it's really hard to get a believing JW to question anything.