You don't need to directly observe something in order to prove that it exists. That notion is a load of hooey propagated by someone with no scientific knowledge or experience.
I have never been to New York City. There's a chance that I might never go. But I have seen ample evidence that it exists that I don't need to actually go there to accept as indisputable fact that it is real.
The key there is evidence. I don't reject the evidence of New York City's existence simply because I don't want to believe that it's not there. If, on the other hand, someone were try to believe that the city of Atlanta doesn't exist, I would take strong exception to that because I've been there and I know firsthand that it does exist.
The problem with Creationists--and the reason it has NO place in a science class--is that they expect people to reject all evidence for a universe billions of years old and all evidence that the Theory of Evolution is correct in favor of another idea for which ZERO evidence exists, an idea for which mountains of evidence in fact disproves. That is the antithesis of science.