Including intelligent design in school curricula would be perfectly acceptable--even as a blatantly religious concept--if the scientific community was split over how we came to be. If there was debate among scientists as to where we come from, then of course it should be included as part of a scientific discourse. But it's not. 99% of scientists think it's bull honkey. There isn't any debate within the scientific community because there is little or no scientific evidence to back it up. The entire concept is based on a fallacy of logic--they came to their conclusion (that 'some intelligent force' created everything as is) and then started looking for evidence that supports it. And their "evidence," as far as I know (since I have not researched the subject particularly deeply), is largely crappy and easily discountable. And, on top of that, it's blatantly religious.
I don't see why they want this taught in school so badly. I mean, if that's how you think things came to be, just tell your kids about it at home. That's why we have freedom of religion...so you can teach your kids whatever you want about who (or what) created the universe. But public school needs to stay secular.