I had doubts, but I grew up in it. My mom got baptized around 1975, but my dad said after yeas of study, that much of the theology in WT does not make sense. He said that WT just invented too much things, but nothing is based on Bible. After couple years of constant pressure from JW relatives, he quit to study and never got baptized.
After my dad's death, I believed that the negative influence on my JW thinking was gone and I was attending like crazy, been on conventions, did field services, etc, but doubt were there. We eventually started to study book Revelation, and I just could not reconcile most the BS in that book with Bible. For example we were talking about pouring of wrath from Rev 16:1 and they said it was some convention in Ohio around 1920. Everyone around me was, awesome - me what BS. I just could not reconcile the book study with what I knew and suddenly came to me that if the material is BS, than the religion is BS. After the book study, I never returned to KH.
WT believes that their existence is outlined in the dooms prophecy; and the best way to justify a prophesy, is to prophesied the past.