There are many reason I grew out of Christianity. Perhaps the most significant one is this.
Christianity claims to have the one truth that is for all humanity for all time. This is based on it's scriptures, core doctrines and theology. It's essential to understanding the work of Christ and to reject it directly challenges the premise that Christ died for all humanity's sins and that the Judeo/Christian god is indeed the one true god of all the universe.
I believed this most of my life and any inklings of doubt were quickly quelled by reminding myself that "who am I to question god's plans", and "his ways are higher than ours" etc.
But ultimately the problem is insurmountable. If this gospel is for every person who ever existed and ever will exist, and is the most important information in the entire universe that determines not only our well-being in the present but also our eternal destiny, then god has failed to achieve this on a scale that is tragic beyond belief.
We are told that it's our responsibility to spread the gospel to all the world.
Can we take seriously the idea that god would put this life and death matter into the hands of the humans he apparently created in the complete foreknowledge that they would fail to do so - and fail on a grand scale!
Did he forget about the billions of people before Jesus? Or did he treat them all with the same disdain he had for those he drowned in the flood?
Did he realise that billions of people in all the countries and nations outside of the middle east throughout all history would never hear this message, let alone understand it's implications?
Did he realise that still, countless billions, through no fault of their own have no idea of this one true god and the way to be saved from our sin and his wrath? Or that billions never will?
"But God's ways are higher than ours!!" Yeah right. I'm not seeing it, despite years of genuine attempts to figure out how this works.
This is the fatal flaw in the whole system. God has failed to deliver the goods. Most of humanity is lost, and possibly in ways that are too horrific to contemplate.
I have not had one single descent response to this - ever. Not even the best theologians I've read have addressed this issue in a rational way. They all end up with "his ways are higher..." etc.
The reality is this - whether we like it or not. Christianity is one particular religion that arose from one particular tribe in one particular region. It had no concept of the world as we now know it. It created a god that fitted their small, primitive world view. It worked for them in that context (although I would even question that). It never was and never will be the one truth that sets all humanity free. But to let go of this delusion is to let go of the basic tenets of the belief system, and that will cause a complete crisis of faith - something that most are terrified to allow.