There is very little verifiable evidence that supports the idea of an intelligent designer. Most of its arguments are tendentious or misleading and many of its proponents are creationists, in effect or in fact. Darwin's theory of evolution has compelling evidence to back it up, persuasive arguments in its favour and, helpfully, faces most of its opposition from loonies.
BUT, the key demand of the Intelligent Designers appears not to be that ID and Darwinism are given equal weight in the curriculum, but that Darwinism not be taught as established fact, but as a persuasive but unverified theory. Now, the theory of evolution is just that: a theory. It cannot be definitively proved as a hypothesis and there are, apparently, certain elements of modern science that sit unhappily with pure Darwinism.
In this context, it is clear that Darwinism isn't, and isn't supposed to be, gospel (so to speak). It should be the duty of every good teacher, from a very early level, to teach pupils how to question concepts, how to recognise the flaws in received wisdom, how to challenge perceived truth. It is a widespread complaint of University tutors (and here I can speak with a little more authority) that increasingly students want to know what the answer is - not seeming to realise that the key role of a tutor is to provide guidance as to what the question is, allowing the student to find out the answer themselves.
In this context, provided that it is taught well, allowing teachers to point out to students that there is an argument to be made on evolution should allow students to look at the data, look at the relative strengths of argument and make up their own minds. Or is that completely unrealistic?