There are two basic arguments on the subject, though only one has any place in a free country:
"The first stage of this education being the schools of the hundreds, wherein the great mass of the people will receive their instruction, the principal foundations of future order will be laid here. Instead, therefore, of putting the Bible and Testament into the hands of the children at an age when their judgments are not sufficiently matured for religious inquiries, their memories may here be stored with the most useful facts"
-- Thomas Jefferson; from 'Notes on Virginia' Query XIV
"Secular schools can never be tolerated because such schools have no religious instruction, and a general moral instruction without a religious foundation is built on air; consequently, all character training and religion must be derived from faith"
-- Adolf Hitler; from remarks at Nazi-Vatican Concordat (Apr. 26, 1933)