Part of the problem here is a dumbing-down of the American public about religion generally.
It is not just in the schools, but public school teachers are (often justifiably) allergic to discussing religion in any way whatsoever. One result is that a whole swath of students grow up and have little understanding of how religion functions in societies, or how religion has shaped American institutions, reform movements, socio-economic strata, etc.
Meanwhile, seminaries all over the country continue to close as Christian church attendance declines, especially in the best-educated denominations. Sunday school has become insipid or has vanished in many places.
White Christian conservatives, meanwhile, have hitched their horses to a highly politicized version of Christianity, including the things Posner and others mention, such as megachurches, dogmatic colleges and universities, etc.
And of course much of what is happening is a massive reaction against what Robert P. Jones called “The End of White Christian America.” It might not change the end result, but it makes getting there–to a non-coercive, racially and religiously diverse nation–far more harrowing.