One thing atheists, even American atheists, should be up front about is, yes, right now Fundies are in the cross hairs, but I think we should predict the understandable hesitancy of liberals who are going to be thinking "first they came for the fundies, then they came for the moderates, and now they're coming for me..." To a certain extent I think there is a veil between present strategies for an immediately better today and what various atheists see for tomorrow. Some people believe that religion and faith, in any guise, will remain a perpetual threat, ready to recrudesce pathologically, and others only hope for a time when religion has been de-fanged and are comfortable with the idea that it can remain a largely benign social adjunct. Even most New Atheists have that view. I think Hitchens may have been an eradicationist.
I don't think that the Gnu Atheists and the confrontationalists, such as three of the "Four Horsemen" (excluding Dennett), Bob Avakian, PZ Myers, Jerry Coyne, and minor authors such as myself, make it a giant secret that the liberals and moderates are subject to the same critique as the fundies. The fundies' assholery is why they're the primary target, but the New Atheist critique is not that they're assholes. The New Atheist critique is that you cannot legitimately ground any moral beliefs, good or bad, in the existence of God. Accommodationists so persistently misunderstand this critique that one might suspect intentional obtusity: it doesn't matter that some religious people ground perfectly good moral beliefs in God; it's the basis that's illegitimate, not the outcome.
And, as a lot of authors have noted, the "liberal" religious are usually not all that liberal. Talk to a supposedly liberal theologian, and it really won't be long until he uses God to justify some very illiberal belief, usually against abortion or homosexuality. Avakian makes this point very strongly in Away with All Gods. If your religion's morality is totally acceptable without God, what job is God doing?
Roberts is perhaps saying that we have historically constructed a lot of Western liberal (in the contemporary sense, not the political science sense) ideas in terms of God and Christianity. Well, sure. But taking God away does not therefore take those ideas away (or if it does, maybe we should). It seems that the scientific truth that we have evolved biologically to be social animals and evolved socially to create complex, interdependent societies provides a reasonable justification for a lot of the rights formerly constructed in terms of God. I think a natural basis for rights is a lot more complicated than a theistic basis, but that's not any more valid an objection than that quantum mechanics is a lot more complicated (and weirder) than classical mechanics. I mean, here we are: we can observe that societies have constructed quite a lot of rights for their members; a scientific theory has to account for observation, n'est pas?