Jeffrey Toobin on ''Cafeteria Government''

Whatever one thinks of Ms. Davis, Jeffrey Toobin's short essay on the New Yorker website  raises some interesting points about whether religious accomodation amounts to "cafeteria citizenship" and even to "cafeteria government". 

If citizens (and now in the US, small business and family-owned corporations thanks to the SCOTUS Hobby Lobby ruling) are free to decline some obligations (eg, to serve customers, to provide certain kinds of health care) on the basis of their religious beliefs, what degree of accomodation should be allowed to government employees?  Is it acceptable for a govrernment to accomodate the beliefs of its employees by allowing them to decline to perform certain tasks, such as issue marriage licenses to same-sex peole, provided that there are other government employees that are willing to perform those same tasks?  What are the limits to such accomodation?  Voluntary military service comes to mind as one government sector where all employees must be willing to perform, enable or at least sanction certain actions, specifically acts of violence at the behest of a lawful authority.  Are there comparable cases where accomodation is not possible in government service?