Sorry for the late reply, I got distracted by stuff
Because we are “fallen”. Ever since the fall, that’s been our nature.
Not just since the fall. If we fell, then because we've been created fallible. I've already told you I find it strange that the creation of a divine being such as the Christian God, the 'crown of creation' even as some like to consider themselves, made in His image no less, and the object of His love, should be so fundamentally wrong.
Concerning the fall and subsequent "saving" of humanity, I could argue - even from a biblical point of view, I think - that humans never fundamentally changed, the only thing that differed is God's opinion of us. The only thing that led to the fall was God planting a very specific and very symbolic tree where Adam and Eve would eventually find it and eat the fruits; the only thing that "saved" us was an entirely symbolic sacrifice enacted by God and His 'son'. In neither case had humanity any agency over their destiny whatsoever, in neither case did they act fundamentally against their nature. It's only ever been God choosing to condemn or save us and justifying it through some symbolic metaphor. This, coming from a religion that often puts an emphasis on free will and the importance of "choosing" God.
That is understandable. Doesn’t it make sense to not be attracted to your enemy? You are at odds with God who promises to punish his enemies. That doesn’t sound nice or kind at all. But may God work in your heart so that you might learn to love Him. Even though, you might be separated from God right now, Christ’s life, death, and resurrection is your assurance that God will accept you with loving embrace as his child. That’s why trusting in Christ’s life, death, and resurrection is so crucial to your salvation.
God is not my enemy, and I am not at odds with Him, for He doesn't exist. I am at odds with people telling me that everything that makes me who I am is wrong except in the light of their own belief, with people telling me I am evil independent of how good or bad my acts are as long as I don't accept a symbolical act they believe in. I am at odds with the arrogance of people considering me a mere recalcitrant child that will eventually feel divine love, just because I don't share their beliefs. I know it's what you believe in, and you don't mean to offend; but please understand that from my perspective, being essentially told "Shush, it's all going to be well" by my interlocutor in a debate just doesn't come across very well.
And sure, if God did exist, I might have issues with Him, though then at least I could directly 'talk' it out with Him, see for myself how things are. But He doesn't, of that I have as little doubt as you have of the contrary. I am not debating because I have some internal quarrel or so, but just because I like to debate; especially since as an atheist I am surrounded by people who think differently. I'm just saying this because sometimes I get the impression that the person I'm talking to assumes that the fact I'm even debating at all means I'm a lost lamb trying to come to terms with doubts but will eventually find the way (meaning
their way). At least I'm certain it's happened before, and it understandably makes me feel like I'm not being taken seriously. Please ignore and excuse this whole paragraph if it doesn't apply to you
Still, maybe that somehow answers your original question: in a way it's both a heart and intellectual issue, though not in the sense you meant it. In my 'heart' I do not believe in any deity, spiritual or supernatural being or force. Intellectually I've yet to hear an argument that might change my mind or make me doubt, and all evidence I've seen so far confirms me in my worldview. And yet I do not reject Christ, because Christ to me is a fictional character, possibly based off of a real but very normal human. I feel as little need to reject Christ as I might feel rejecting Gandalf, if that makes any sense.