The following is a brief summary of an argument I make in more detail in my book Thou Shalt Not Believe.
My problem with the Christian teaching of sin is not that it recognizes that people have a natural tendency to harm others, treat other people as means to their own ends, seek power over others, and indulge their carnal appetites. I agree with Christianity that people have these tendencies and that they are an intrinsic part of human nature. What I don’t agree with is that humans are responsible for this state of affairs.
Humans have these tendencies for natural, biological reasons, not because they or any of their fellow humans rebelled against the creator of the universe. At least that is what the best available evidence suggests.
In order for the teaching of sin to be true, it would be necessary for the creation stories in Genesis to be true at least to the extent of teaching that the first humans rebelled against God and the rest of Genesis and indeed the whole Bible would have to be true at least to the extent that they teach that all subsequent humans also rebelled and continue to rebel against God (or in other words that no people are righteous, as Paul unambiguously held).
However, the best available evidence suggests that the creation stories in the Book of Genesis are mythological and have little to no basis in historical fact, for the best evidence shows that modern humans originated in East Africa around 100,000 years ago, not in Mesopotamia or anywhere else in the Near East.
In addition, archaeological evidence strongly suggests that humans have always participated in a significant amount of internecine violence and, more importantly, biological evidence shows that our closest relative, that is, the species with which we share the most recent common ancestor – chimpanzees – fight with each other over territory and for pride-related purposes all the time.
Put simply, all of the tendencies normally associated with human sin or sinfulness can be found in the animal kingdom. The biosphere is adversarial between species, competitive within and between species, and features cooperation only when it is in the mutual self-interest of each participating organism. That humans have inherited their tendencies ordinarily associated with sin from nature is a far more reasonable explanation than the teaching of sin.
Furthermore, if human sin existed and an omnipotent and omniscient deity created the universe, that deity would then be responsible for the existence of sin, not humans. Even if that deity had intentionally allowed for sin by giving humans free will, he/she/it necessarily would have known ahead of time that humans would use their free will to sin, thus making the deity ultimately responsible for the existence of sin.
In addition, if eternal damnation is the consequence of sin, as I believe the New Testament unambiguously teaches it is for those who do not accept Jesus as their savior and his crucifixion as the atoning sacrifice (or, depending on one’s view or the passage on is citing, ransom) for their sins, then this would mean that the deity was necessarily responsible for the eternal damnation of all people who were unregenerate sinners by the standards the deity set up to begin with.
This is my most fundamental objection to Christianity. It is an objection to (what I regard as) the corollary teachings of sin and hell. This objection is not to a caricatured version of Christianity – it is to the very core of what Biblical Christianity is and has always been and applies equally to Protestantism, Roman Catholicism, the Orthodox churches, and all other traditions of Christianity which ultimately purport to be based on the Bible (rather than, say, the Bible and the writings of some later alleged prophet whose works are given an equal status to the Bible).
This objection means that I don’t believe a redeemer for the human race was ever necessary. As such, if my objection is valid, it undermines the very foundations of the Christian religion, not merely a caricatured version of it, for if no redeemer was ever necessary then it was never necessary for God to incarnate on earth as Jesus Christ to be the atoning sacrifice or ransom for human sin.
Furthermore, this objection means that I deny that there is any evidence for the reality of eternal damnation (or the second death) and because I deny the truth of the rationale for eternal damnation found in the Bible and Christian tradition, namely the doctrine of sin – whether conceptualized as original sin, personal sin, both, or another type – I deny that the teaching of the logical necessity of damnation found in Christian tradition has any basis. As such, I do not regard eternal life (or heaven) and eternal death as the only two ultimate alternatives.
Even if people can have eternal life by accepting Jesus and thereafter receiving the Holy Spirit, I do not concern myself with this aspect of the Christian message except to state that I have no experiential evidence of any kind (whether based on sensory experience, mystical experience, emotional experience, alleged historical evidence for the resurrection, or anything else) that it is true and therefore I don’t believe it.
I also don’t agree that the state of affairs described in the first paragraph is immoral by any objective or universal standard, as I deny that an objective or universal standard of morality exists. I will discuss why in a separate post at a later date.