A Work In Progress - I think this is a good rough draft, I'll refine it over time, add references, links, and citations. In the meantime, feel free to help me by pointing out any errors or defeating arguments (or even just linking to other resources in the comments).
But here are a few foundations for my Nonbelief:
If "objective moral values and duties exist" then the question of god is irrelevant because, being objective, they cannot depend upon god. They would have to exist as facts of the matter, independent from any god, or else they are not objective. This argument is the same as saying 'if matter objectively exists, then god". It is a non sequitur.
Nor do I grant that objective morals exist. All evidence is that we follow something closer to empirical consensualism (the proposition that, I and others have a say in the nonsense you try to pull on us which we can legitimately base on the facts of the matter). I believe that GIVEN THE HUMAN CONDITION (which by definition means we're not talking about the objective - a human who, for example, lacks a sense of empathy would not likely share our values) that there are moral imperatives that we can discern through observation. I believe there are good, empirical arguments to be made for such imperatives but ultimately they depend on shared values. If we cannot agree on a value position then we will not agree on the conclusions regarding ethics or morality. Nor does a morality existing necessarily imply that there is some arbiter of them. They are JUST principles of behavior. Some behaviors we don't always like, but we tolerate in others (belief in religion, free speech, non-belief in religion, blasphemy). Other behaviors we find so contrary to human existence that we're willing to enforce them upon others, even when we're not directly affected (murder, theft, assault, rape, fraud, child abuse, slavery, etc).
Slavery is one of the best arguments against the Bible as a source of moral authority. I will let Marvin Wheat make that point for me: "emancipationism [or] abolitionism is atheism" 'The progress and intelligence of Americans', Marvin T. Wheat. Bravo Mr. Wheat, I couldn't have said it better. The rejection of slavery is the rejection of the Judeo-Christian values that underlie it (neither group invented slavery, they merely codified as if it was the will of god). This Atheism is the claim that we have grown beyond the narrow-minded claims of iron age, theocratic despots asserting their power and exploiting the ignorant/uneducated/undereducated masses of the time. Yes, I Very Well understand the draw - for a finite payment today, and draw from infinite perfection tomorrow - you know, after you're dead so we don't have to actually prove anything. And the bad people will get punished (since we failed to hold them responsible) and the "good people" (defined invariably by EVERYONE as those on YOUR side, it's always the other guys who are evil) will be rewarded. Oh, and it's conveniently undetectable and unprovable (despite 1 Kings 18), so you'll just have to take their word for it. I mean, nobody would Die for a false belief would they? (*cough* 9/11 *cough*, Opps, deploy the Special Pleading police to clean that one up). And let's ignore the fact that it's not REALLY the bad people who are punished, they merely have to confess their sins and accept Jesus and get a Free Pass. It's those evil atheists who want to take responsibility for their OWN sins and not scapegoat them through a Human Sacrifice that will receive infinite punishment for their finite transgressions against the make-believe. What god really hates is someone who thinks for themselves, not the murderer, or the rapist, or the child abuser.
But a bare and unsupported assertion that ones moral claims are grounded in their god is fatuous and empty. You must provide and argument or demonstration as to why your claims of moral ground in YOUR God are substantial, whereas all the other tens of thousands of such claimants are in error.
The fact is that the religious methodology (be it revelation, gnosis, or otherwise) is wholly unreliable and demonstrably leads to mutually exclusive conclusions. I might as well be a Scientologist or Mormon or follower of Jim Jones or Sai Baba as all such claims rest on the same, deeply flawed, methodological footing (that of making things up and deciding to believe in them ON the absence of evidence and contrary to all rationality).
What Passes For Biblical 'Morality'
On Christianity, what one must accept is that commanding someone to murder their own child is a moral action (if not, then god is immoral; or if it's moral for god to do it and it's not moral for you then it is NOT an objective standard). And if you argue that it was ok because God stayed Abraham's hand then you fail to account for the thousands of infants murdered by and on account of God: The first born of Egypt; in the presupposed flood; by the Israeli soldiers against the Amalekites, the Hittites, the Girgashites, the Amorites, the Canaanites, the Perizzites, the Hivites, and the Jebusites; or amongst the 100,000 Syrians; or the 1 million Ethiopians; etc (2,476,636 in total explicitly numbered in the Bible, which doesn't account for the flood or first born or many other mass murders and genocides in the bible). God doesn't care much about the lives of humans, infant or otherwise.
Even if you presume the Canaanite (et al.) adults deserved genocide (which is a prejudiced and abhorrent conclusion to begin with, and is baseless in fact), there is no argument by which you can convince me that it was thus a good and moral action for the poor Israeli soldiers to also slice open the children with a sword. Such murders (presuming they actually occurred, which also fails the factual history test) would be immoral. Period. Inexcusable. I DARE you to pick up a sword in your hands and hold it over an infant and even CONTEMPLATE bringing that sword down with force. If it doesn't make you ill just thinking about it then you need mental help because you are abnormal.
The Bible shows every evidence of being plagiarized from older mythologies and events from history (e.g., from Gilgamesh, Judas the Galilean, Egyptian sources, etc).
The utter lack of contemporaneous corroborating historical accounts is also devastating to the claims. Nobody else thought to mention the graves opening up and the dead walking among the living? Josephus was far too late (and either plagiarized or dishonestly modified), Matthew, Mark, Luke, and John were TOO late, written anonymously, and we have every reason to suspect them (ask any Jewish scholar for their opinion of Christian re-interpretation of their own works). The Church's violent suppression of dissenting voices (just ask the Arian's) and destruction of contradictory evidence likewise condemns them. And then the Church, as further evidence of their systemic (commanded by the authority of the Church) immorality, for the next 1700 some-odd-years rules via murder, torture, and intimidation and destroys innumerable cultures around the globe under the pretense that it is God's Will (Manifest Destiny, Requerimiento, etc).
And please do not try to pretend like Protestants escape any of this, read Luther's 'On the Jews and their Lies' and 'In Bondage Of The Will' for starters. Then we can move to the Thomas More / William Tyndale screeds against each others respective religion. Calvin's vicious theocracy is likewise well documented (cf. Michael Servetus).
In the end it doesn't matter if there was a historical personage that the character of Jesus was based on or not. It is irrelevant to the question. I think the best evidence argues for an amalgamation (especially the evidence for Judas the Galilean). You can legitimately disagree because there is no conclusive evidence. Claiming the Biblical texts as prima facie evidence for Jesus buys you no more than the prima facie evidence for the gods in the Hellenistic texts. Once again, the religious methodological failure is fantastic and profound.
Scientific methodologies converge on answers while religious methodologies obfuscate, diverge, and bifurcate.