Whether or not it was "right" for Amanda to resign is up to her and Edwards. I agree with SteveG: Edwards crashed and burned by not anticipating that the right would Swiftboat any choice of blogger and failing to take steps to counter the threat before he even announced his choice. In other words, "They couldn't hit an elephant from ..." Edwards is presently too naive to deserve my vote.
But unless I'm missing some irony, I'm surprised by Marsh's apparent assertion that Amanda's comments were somehow out of line.
In her review of Children of Men, Amanda says,
The Christian version of the virgin birth is generally interpreted as super-patriarchal, where god is viewed as so powerful he can impregnate without befouling himself by touching a woman, and women are nothing but vessels.Marsh responds,
I couldn't believe my eyes... It goes too far... Talk about handing your opponents the knife.
I'm an atheist, so I don't have any qualms at all about reinterpreting scripture; I myself simply reinterpret all religious scripture to be pure historical fiction. As a self-described "religious" (perhaps "spiritual") person and obviously liberal and humanistic, Marsh too has presumably reinterpreted scripture to support a benign modern ethic. Good for her. Such an interpretation has to throw out the literal meaning of 98% of Christian scripture. Again, good for her: I can hardly object to her throwing out 98% when I throw out 100%.
But to assume that her interpretation is in any way authoritative is nonsense. (Even with the utmost charity, I just can't see any other logical interpretation.) Amanda's comments present historical and present fact. Christianity has been one of the worst, possibly the very worst, misogynist social constructs ever known to humanity. (Islam is catching up fast, but Christianity has had a thousand-year head start.) The dichotomy between Eve's "corruption" of humanity and Mary's virginity is a fundamental basis of Christianity's historical and present misogynist narrative. Amanda does nothing but point out this blatantly obvious fact.
Marsh's post is an example of the second reason why I'm generally unsympathetic to religious "moderates". (I explore the first reason, privileging faulty reasoning, in my commentary on the Sullivan/Harris debate.) It seems that because their own interpretation of scripture is benign, they condemn criticism, however well-grounded in actual fact, of anyone else's interpretation of that scripture.
Such condemnation is often explained by asserting that some particular culture is at fault, not the religion. The problem is that it's all culture. There's just no such thing as "religion": All religion qua religion is merely a set of null, meaningless slogans. By self-identifing as a Christian, Marsh apparently buys into the culture of self-identified Christians. By declaring Amanda's comments "too much", she is implicitly defending the the Christian culture she has bought into, including the blatantly misogynist segments.
It would be fallacious to conclude that because Marsh (or anyone else) self-identifies as Christian, she must therefore be misogynist. I take Marsh at her word that she is a feminist. And good for her. But her personal interpretation of Christianity, admirable though it is, is beside the point.
In the same way, just because I personally renounce imperialism, I cannot say that the United States is therefore not an imperialist nation. I can say only to those who criticize the United States, "Yes, it is indeed an imperialist nation, deserving of your disapproval, but some of us do in fact dissent and are working against it." Acknowledging criticism is not the same as disloyalty.
If we are to exclude from the political process everyone who has criticized Christianity and the Catholic church for its misogyny and anti-feminism, merely because some feminists hold a minority interpretation of scripture, we won't have any honest feminists--feminists who don't ignore the "elephant in the living room" of Christianity's millennial pervasive misogyny--in the political process at all.
Update: On good advice from a reader, I should note that Marsh does in fact acknowledge the serious feminist issues in religion, saying,
I have also written about what The Church, which I refer to in capital letters to encompass religion on the whole, has demanded of modern women. Subservience. Tradition. Perfection. Standards I've failed to meet. There is little space for modern women in most religions today.As I noted in the original essay, Marsh pushes this criticism off to culture (i.e. to the supposedly pious, implying her interpretation is authoritative).
But what "abject disrespect" does Amanda offer to "what The Church symbolizes to some of us?" Except, perhaps, that's she's criticizing the The Church from the outside.
The Church has historically done more than merely demand subservience. It has literally demonized women, making women and women's sexuality not only subservient, but positively evil. How is Amanda's use of the word "befouling" (the only word I can see that might even remotely be considered intemperate) do anything but accurately capture this obvious historical truth?
If, for instance, Andrew Sullivan were to assert that torture "befouled" America, I would not consider that in any way disrespectful towards the good things that America (perhaps naively) symbolizes to me.
It's a sad but hardly surprising commentary on today's (supposedly) secular society that Amanda, who appears to hold "The Church" in almost as much contempt as Thomas Jefferson, is deemed unsuitable to work for a (supposedly) liberal presidential candidate--by another liberal.
 "Millions of innocent men, women and children, since the introduction of Christianity, have been burned, tortured, fined and imprisoned. What has been the effect of this coercion? To make half the world fools and half hypocrites; to support roguery and error all over the world." Notes on Virginia