So, on what will we hang our hat on once we've decided that religion --- or more specifically the 'judeo-christian umbrella' --- is sanctioned by the state in regards to prayer in schools, the 10 commandments on public buildings and public displays of religion on community ground. These things are all trivial in themselves (although for some people, putting little kids in the position of having to pray or abstain is unconcionable.) But regardless of whether each little instance of religious tradition in the public square is in itself pernicious, taken together, if sanctified by the courts, it erodes one of the basic tenets of our system, which is the prohibition against the establishment of state religion. And that adds up to a greenlight to teach creationism or promote any other Christian dogma --- with my tax dollars.
Are these sorts of things really trivial, though? Official recognition of one religious tradition, even one as broad and common as Western monotheism, as 'the' civil religious tradition still excludes other traditions, and reduces their members to a second-class status, permitted residents of a monotheist society rather than citizens with full equality in the eyes of the law. The rights of social minorities are then no longer guaranteed by the foundational principles of the state, but by the pleasure of the majority to permit the minority to continue to exist. Recognizing the Ten Commandments as the foundation of our legal system, even just ceremonially, serves to undermine the notion that a Buddhist automatically has the same legal rights as a Christian. Which is, of course, precisely the opposite of the intention of the Establishment Clause, and the goal of the wingnuts: theocracy.