I would have no problem with ID being taught along with evolution if it was taught properly and fully. This would include arguments against it, it could be a good learning experience and maybe keep kids away from other pseudo-science.
But our schools don't have the time or resources to waste on such a class lesson, as they can't even teach current science correctly.
I sometimes think IDists realize this. Stickers in books or even small blurbs are beneficial to ID. A full blown course taught next to a full blown course of evolution would end with ID being blown out of the water. Just like creationism or politics, intelligent Design is a sound-bite science and falls apart under scrutiny.
[Side]Apple's spell checker keeps trying to turn "IDists" into "Idiots." I have a smart computer.

[/side]