In the Sullivan/Harris debate, Sullivan has time and again--at least to the careful reader--exposed the utter vacuity of his specifically theistic belief. Having transferred his superstitious magical thinking to conservatism, Sullivan has left to "God" specific ideology, no actual content at all, just feel-good platitudes. Sullivan can have his private "truth" about God, and allow others their private "truths" about God, because none of these truths actually matter.
But most readers have neither the time nor the inclination to read so carefully, and Sullivan is almost unmatched for his talent in making the vacuous sound good, very good. Even when he's right, as on gay marriage and torture, he's right about the blatantly obvious, where sincerity and rhetoric count for so much and analysis for so little. At the end of the day, I don't think Harris is a good enough writer to overcome Sullivan.
Someone in the atheist camp needs to match Sullivan's sincerity and rhetorical force. More importantly, we need to perform some emotional and psychological judo. We need to warmly accept all the lovey-dovey feel-good emotionalism, and show how it's not only compatible with atheism, atheism makes it better.
I'm doing my best, but my talent and training are less oriented to singing rhetoric and more to computer manuals, and I need years more practice.
We need a poet. Sam Harris is a lot of things, many of them good, but he's not a poet.