Depends entierly on the atheist. Some start from a Buddhist background. In fact, so ARE Buddhists. (My main problem with Buddhism is that all the arguments are phrased in terms of inevitable reincarnation of something...Buddha was a bit opaque about just what, so I'm not certain that I can't believe it, but I'm sure not certain that I can.)
My personal problem has to do with the nature of the evidence, and the unreliability of even disinterested eye-witness testimony. The only gods I'm certain of are those that I've encountered (I *think* they're the same things that others have called gods), and they appear to be mental phenomena. (I'd say psychic, but that term has been so misused that it would be even more likely to be misunderstood.) They appear to be sub-linguistic mental phenomena that are probably the same things that Jung called archetypes. The roots from which all mental functioning is buit. These features seem to be shared by many (all?) people, though it's hard to be sure, and some of them even seem to be shared with other mammals. (Well, dogs to be specific. I don't understand cats well enough to comment about them, and the evidence is quite weak even for dogs...being more along the lies of "consistent with the theory" than "experimental proof", but then that's true even for other people.)
Also, your attribution of certain beliefs as originating with Christianity is highly suspect. Many Christian practices and beliefs came from Mithraism. Others from Judism. And Others from Hellenistic Greek philosophy. Just how much originated with Christianity is extremely dubious if, in fact, anything did except a bit of clever phrasing and some political tactics. Certainly the equality of people before the gods was neither unique with Christianity, nor universally held by Christians. (See, for one example, "The Divine Right of Kings". It was also held in many times and [Christian] places that the more powerful were more loved by god. The Puritans, e.g, made it explicit. "Material success the the manifest sign of divine favor." That's not an exact qoute, as far as I know, but it could be.)