If the parents have no right to control the content of education then the government should have no right to force them to pay for it. It is taxation without representation, the stuff of revolution if History serves.
The parents can elect representatives that will change the laws and change the curriculum. The court is saying that individual parents don't have the constitutional right to pick and choose what a school teaches their children.
I assume they have the right to take their children out of public school, and put them in private school or home-school.
If we keep getting rulings like this, it should help the push for vouchers, which are the real solution. We will NEVER get public schools to cater to the whims of all parents, I bet that even among conservatives we would have a huge fight over prayer in schools and teaching evolution, for example.
Vouchers meet the need for universal access to schooling, without forcing a one-size-fits-all solution.