I’m sorry what the Christian groups put you through.
If this is what they do to Christians, who presumably are “their own” or “God’s chosen” or whatever, imagine what they do to non-Christians when they get their hands on them. Well, we don’t need to imagine, we know.
Reading your article, it seems to me the question you pose has a much simpler and universal answer. Why do so many people seem to hate Christianity? Because Christianity seems to hate so many people! It wasn’t explicit in my mind, but my assumption until now was that they “only” hated non-Christians, but it is clear from your experience (and those of others) that their hatred can extend to other members of their own religion as well. I guess abuse begets abuse, hatred begets hatred, so the cycle perpetuates itself.
Of course, this applies to most religions, not just Christianity, with possible exceptions like Tibetan Buddhism and some “naturist” religious belief systems. On the other hand, it is entirely possible that the so-called exceptions simply haven’t had an opportunity to wreak large scale havoc, yet.