Fairness in Religion in Schools

H/T Scott Hedges for drawing my attention to this organisation, which supports secularism in Australia (more specifically, Victoria) at the level of state schools. We might well wonder why religious organisations are given the chance to teach devotional classes to the children of their respective congregations - or, probably more often, people who are merely deemed to be from their respective congregations.

While this practice is well entrenched by now, and, to be honest, I am sceptical as to how much effect it really has on the religiosity of our society - scripture classes were not taken very seriously by most students when I was at school, and I doubt that that's changed - there's an important question of principle here. Why, exactly, are schools run by the state doing anything other than teaching secular knowledge? Why shouldn't any doctrinal classes be provided by churches, mosques, religious parents, etc., outside of school hours?

Obviously, there's a history to it (I'm currently reading an interesting article by Catherine Byrne that goes into this aspect of public education in Australia in considerable detail), but it's hardly something that would be easy to justify if we were starting over again.