God and the Science Classroom

In a recent interview with the Nashua Telegraph, Republican presidential candidate Rick Santorum was asked about teaching creationism in schools.  In a familiar tone, Santorum claimed that there is a fear, on the left and in the scientific community, of talking about God in the science classroom because of a kind of political correctness, and a sense that, in spite of its awesome explanatory power, the notion of a creator has been arbitrarily considered off-limits to inquiry.  Here's his exact quote:

There are many on the left and in the "scientific community," so to speak, who are afraid of that discussion because oh my goodness you might mention the word, God-forbid, “God” in the classroom, or “Creator,” or that there may be some things that are inexplainable by nature where there may be, where it’s better explained by a Creator, of course we can’t have that discussion. It’s very interesting that you have a situation that science will only allow things in the classroom that are consistent with a non-Creator idea of how we got here, as if somehow or another that’s scientific. Well maybe the science points to the fact that maybe science doesn’t explain all these things. And if it does point to that, why don’t you pursue that? But you can’t because it’s not science, but if science is pointing you there how can you say it’s not science? It’s worth the debate.

There is, of course, nothing surprising about Santorum's argument, he's made it many times before.  Science curricula are probably not terribly threatened by his candidacy -- he's polling in single digits at present -- but still, his views reflect those of a large section of our country, and the question is often posed.  Why, exactly, can't God be a part of the equation when it comes to science classes?