I'm familiar with Ehrman's book and with the mythicists' evisceration of it. Ehrman invents early independent sources for Jesus out of thin air by arbitrarily positing layers within the physical ones we have. Very dubious. He says the early Christians were influenced by Judaism, not by Greco-Roman religions, as though Judaism at the time weren’t part of the Hellenistic world. He appeals to the criterion of embarrassment, which either projects modern sensibilities onto the ancient authors or mistakes allegory or metaphor for literality. For example, was it embarrassing to have only women at the empty tomb? Not if the empty tomb story was intended to subvert pagan stories in which women were prominent (Isis healing Osiris, etc.)
Indeed, Ehrman is an ex-fundamentalist. His insider knowledge can be valuable, but who's to say whether that extreme past still impacts his judgment on Christianity? I've seen many of his debates, and it's odd that he gets so emotional. His previous fundamentalist faith seems to arbitrarily limit his skepticism.
In any case, I’m not saying the Christ myth theory is proven or even very probably true. It’s a toss-up for me whether Jesus was historical, and very little turns on the decision for an atheist.
No, the second paragraph isn't about miracles. It's about the problematic nature of the sources. For example, there's the synoptic problem, so the gospels aren't nearly as independent as they seem or as the NT presents them by assigning them the names of those apostles. This is why there’s no great need to decide whether Jesus was historical. We would know so little about the historical founder because the available evidence is exceedingly problematic.
If God came to Earth as a human, why should we expect that many people would recognize and follow him? Aren't we supposed to be in a fallen state? Isn't that why most people still reject Christianity? Your claim is quite unfalsifiable. If hardly anyone accepts Christianity, you can blame it on original sin and on the devil's temptations. If lots of people accept Christianity, you can say it's a miracle and a sign of God's grace and omnipotence. Either way, this isn't what we'd expect on the hypothesis of monotheism. There should be no sin, doubt, suffering, rejection of God, or need for a theodicy at all. Let's not pretend monotheism is a scientific hypothesis.
The early church fathers promoted allegorical readings before Christianity became Rome's religion for totalitarian purposes. The question isn't about protecting the religion's integrity. What’s suspicious is the pattern in what was excluded and what became canonical. Gnosticism was deemed heretical because it promoted freedom of thought and intellectual responsibilities for each Christian. Catholicism promoted deference to the institution and to the elites who ran a certain social hierarchy. The latter was more useful for political purposes and for sustaining a long-lasting, oppressive organization.
But to say this makes for a coherent religious worldview is preposterous. Jesus said the world was going to end soon, so there should have been no need for such Machiavellian, long-term compromises. And Jesus in the gospels divides the inner from the outer circles, the esoteric from the exoteric. He said those who have ears to hear would understand his hidden message. So Christians themselves should expect divisions within Christianity. By extinguishing the Gnostics, the Church repudiated Jesus’ insistence that he taught secrets only to an inner circle, not to the masses who couldn’t see beyond the parable’s surface meaning.
