From a scientific standpoint, Darwin's theory is as much of a theory as intelligent design. The theory of intelligent design states that "something so complex appears to have been designed by some other force as opposed to pure probablity and statistics". I't doesent advocate any particular religion. If it does, then it should be unconstitutional.
To remove a line of theory or though without first disproving it, is doing a disservice to those who are being presented with "possibilities". To me, barring a discussion of intelligent design in school is stupid because it is the willfull censorship of a possibility/theory. This robs students of the study of another unproven possibility. Darwin's theory is no more proven than the story of Genesis by the way.
Both should be presented.
But what if an explaination is contrived in such a way that prevents it being even potentially disproven? For example the theory that lightning is caused by invisible and undetectable beings is contrived in such a way that it can't possibly be ever disproven.