Apparently as Richard points out the big complaint here is that the course breaks the strangle hold on religious information that the parents'/parents' choice of religion has on that young mind.

Naturally the best way to indoctrinate a mind into a specific way of thinking is to isolate it from all other thoughts and ideologies. So if the schools are forced by law to teach the ideas held in common or in isolation of other faiths then this can only undermine the indoctrinal aspect of religion.

You would think that if the truth claims of their religion was strong enough then what does it matter what they learn of other religions?

this class is like showing a teenager who has never known anything other than the four walls of his bedroom, beaches, cities, ruins, mountains... the child is never going to be content with his bedroom ever again. and the parents and the church know this.

expelling the child however is not a good solution as all this will do is continue their ignorance.