I guess I can't say I have left the org yet, though I have left mentally. Like others that have posted the process for me is the "pack of cards" effect (I'm still on my journey).
1. The first thing was accepting that I had been born into the "truth" and was gay, then realising that everything I had read in the literature about homosexuality was, basically, crap. No support for gay "born ins". Most literature experiences related to promiscuous, drug-addicted cross dressers who came into the truth and then were "cured" (i.e. got married and had umpteen kids). I knew from my research that there is not one documented example of scientific proof that anyone has been abole to change from being homosexual to heterosexual - even if they had managed to change their behaviour. Even though the org's attitude softened somewhat more recently (and has now apparently toughened again), I realised that any acknowledgment by the GB that there were gay people being born in the truth, who hadn't chosen a "lifestyle" etc was either never going to happen or is a long way off.
2. It took a long time for the implications of the above to sink in. Once it did, I realised if the printed material about "gays" was wrong, what else was wrong?
3. The idea of "shunning" disfellowshipped ones was completely alien to everything I felt morally. Despite the fact I thought the Bible supported it (now I know that's not necessarily the case), I couldn't get my head or my heart around it. Also two of my closest friends fell away from the truth (not difellowshipped) and suddenly everything they did in their lives (one got married to a non-JW and now has three lovely kids) was spoken of by JWs with an edge of suspicion and judgement. I couldn't "not" keep in touch with them. They were my friends whether they were "in the truth" or not.
4. Despite on the whole having no personal issues or conflicts with elders or others, I had long felt that the normal every day "busy-bodying" just isn't christian. The group of friends I was (am) left with in the "truth", despite being lovely in most ways, talk about their friends' and even their family's welfare in terms of whether they go out on the field service or get to every meeting. This really really annoys me. If I ask after someone I am not asking for a report on their "spirituality". I couldn't careless about that - it's none of my business. I just want to know if they are in good health and happy.
5. Ray Franz's Crisis of Conscience confirmed to me what I already knew (see 1 and 2 above). I had come across the redefining of "fornication" in the 70s from my research into homosexuality in the literature, but the experience of the woman from South Africa who was disfellowshipped for re-marrying after divorcing her first husband even though he had had anal sex with a woman (which wasn't considered fornication at the time)....How could Jesus be directing this kinds of ridiculousness?
6. The failed predictions hadn't really been an issue for me - I had always swallowed the org's blurb on that (the "some witnesses were over enthusiastic" argument). But it was the GB's attitude to reporting this stuff - blaming the rank and file witnesses for believing it - that really gets to me.
7. Researching the "cross". While I totally accepted that veneration of the cross is wrong and unscriptural, I realised there were absolutely no grounds to be dogmatic that Jesus died on a stake and not a cross. Basically no one can be absolutely sure either way.
8. Realising that much of the "evidence" in the Reasoning book about the Last Days is quoted out of context or completely made up. For instance there is no evidence that the number or seriousness of earthquakes have increased since 1914. I was brought up to belive that the numbe in the last days outnumbered all earthquakes in precending history. This is simply not true.
That's just for starters...