The key to science's success during the hundreds of years since The Enlightenment has been skepticism (in the scientific sense), rationalism, empiricism, and naturalism, as best embodied by the scientific method. I've included a diagram of the scientific method from this website. This method is a predominant reason for why we have achieved the technological progress as a species that we have today.
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The green oval is a lynchpin of the whole thing. Every theory in hard science must be falsifiable by natural evidence - there must be the potential for the theory to be demonstrated wrong in the natural physical world. For instance, if we found some fossils that were significantly out of line with Darwin's theory, then that would be cause for us to look at the new evidence and refine the theory of evolution so that it is improved and once again encompasses the overwhelming majority of evidence. The theory would change since we found out that it was wrong to some degree (small or big) by looking around in the natural world.
Intelligent design/creationism is not science because it are not falsifiable. Period. Full stop. End of discussion. This like explaining why a giraffe is not a piece of fruit. (Don't be confused about the fact that intelligent design and creationism are the same thing – comment if you'd care for a discussion on that which includes a hilarious and embarrassing piece of evidence.)
For that reason, those claims do not belong in the science classroom. Some other classroom, sure, but the claims are simply not science since they are not susceptible to contradiction. They are "invincible" in that sense: how do you test intelligent design? How could anyone ever prove that the world was not created by a higher intelligence? There's no way to do such a thing. This is why Dr. Philip Pettit, Dr. Daniel Dennet, and Kathleen Kennedy Townsend J.D. call intelligent design "not a research programme", "propaganda", and "a distraction". A higher intelligence means "supernatural" as far as humanity is concerned and that means outside of the boundaries of science. Sure, maybe someday science will identify a higher intelligence that we can actually interact with in some way within the natural world. But until then such discussions are inappropriate (indeed, fruitless) in scientific disciplines.
Stein attempts to frame this whole movie as a freedom of speech "battle." The authors who are putting forward creationism/intelligent design as science have been spurned from the science community and had their submitted articles rejected since they have abandoned an essential pillar of scientific practice, falsifiability. This is not a free speech issue in anyway. These are professionals who are being held accountable for their speech in a purely professional way. It means something to be a scientist, and if your writings contradict the very foundations of science, then your participation will not be welcomed in that community. The same thing would happen in any professional community; if a lawyer seriously misrepresented a client or lied in court, they would be ousted or even jailed.
For this abuse of his (false) authority, perversion of the issue of freedom of speech, and blatant pandering, Ben Stein has fallen from my list of enjoyable celebrities. Expelled indeed.