I find your whole line of argument to be pretty frail and ignorant, I wouldn't bar you from being able to work though.

If you don't see how this kind of system would be abused you have a very peculiar perspective on life.

Who said anything about barring anyone from work?

It is a specific employer choosing to question someone on their voluntary relationship with facts.

How is it that people insisting on believing in provable falsehoods (not religious beliefs) is somehow a protected class?

There is also nothing preventing a flat-earther employer setting up the same filter with the opposite polarity, i.e., filtering out people who actively work with scientific principles, perhaps because he considers that science-minded people are less likely to follow direction. It's his choice.

Real example, a lawsuit in Connecticut affirmed that a police department was within its rights to deny employment to a candidate who scored too HIGH on their intelligence test.