[Sullivan's and Will Saletan's] arguments about abortion emphasize moral agreements with anti-choicers, not legal disagreements. Sullivan claiming that she can't be described as pro-choice implies that pro-choicers can't disagree about the morality of abortion, and of course asserting that everyone has to acknowledge that abortion is icky is central to Saletan's shtick.
Good coalition-building on reproductive freedom would consist of emphasizing agreement (the stupidities and inequities of using inevitably arbitrary state coercion to force women to bring pregnancies to term, the greater effectiveness of the broad panoply of pro-choice policies in reducing abortion rates by reducing unwanted pregnancies) and de-emphasizing moral conflicts. .. Acknowledging that many people find abortion immoral can be the start of a pro-choice argument, but it can't be the end of one.
This may or may not be right, but it's sort of beside the point. As Dayo noted, Sullivan's book isn't trying to demonstrate how pro-choicers can broaden their appeal--it's trying to demonstrate how the Democratic Party can broaden its appeal to people who aren't pro-choice. Reading the chapter of the book that discusses abortion, it's clear that she believes (rightly, I think) that most people's views on abortion are fairly well set, but that it's easier to change minds about the relative salience of various issues. To reach voters who are opposed to abortion but who hold liberal economic views, Sullivan writes, Democrats first have to "pass the cultural threshold" with them. One way to do this is going to be for Democratic politicians to emphasize their moral qualms about abortion. This might make the minority of people who lack such moral qualms uneasy, but for better or for worse, at the federal level, the fortunes of the pro-choice movement are tightly bound to the fortunes of the Democratic Party, so pro-choicers benefit when Democrats can find ways to expand their electoral coalition.