Insofar as it is in the interest of a free and prosperous people to promote and instill virtue, I do not find it outside the realm of possibility that an atheist could fall into line at least from a sense of self-preservation. But a civil society is much better served when its participants act out of more than self-preservation, seeking the betterment of all. This is partly, if not largely, why we [the citizenry of the USA] argue over the manner and degree of affirming the common good. Pure self-interest is unhealthy and not in accord with the Judeo-Christian ethic that serves our founding principles as expressed and enforceable by law. Most atheists I know seek to question and undermine this very thing, but not all.
Our Judeo-Christian sensibility responds to “endowed by their Creator with certain unalienable rights...”
An atheist can only appeal to “we decided these were rights”...
And if one group of leaders can decide them some other leader in the future can undecide them.