People have been noting for years that voucher programs, which taken in the abstract might seem like a good idea, are usually just thinly disguised attempts to give money to Christian private schools. The supporters of them often come up with a lot of fancy sounding ideas that make it sound like it's "increasing choice" or whatever, but then cases like this come up and it's obvious that they don't care about choice. What they want is for everyone's tax dollars to go to sectarian, Christian education.
This type of conflict seems to come up any time one of these "religion in education" situations comes up. The problem is that the conservative type of Christians that support this are also unlikely to want forced education of any type that doesn't match their religious beliefs -- even other sects of Christianity, much less Islam.
The situation is not improved by the fundamentalist and right-wing narratives about the founding of the country that are fed to the less-knowledgeable in their ranks. A frightening number of people believe that the founding fathers intended to create a Christian nation and that the 1st Amendment's only real purpose was to prevent the federal government from elevating one sect of Christianity above the others, and to prevent any Protestant denominations from being outlawed. The "religious test" clause was obviously not intended to allow non-Christians into the government, but just to prevent banning of any Protestant denominations. And so on.