ID should not be taught as Science. However, there should be an area of scientific research dedicated to it in trying to figure out if the spirit exists.
Since such a large percentage of people believe in a spirit and even a great spirit (god), ongoing and serious research into this field is more than justified.
A foundation of serious scientific study into this area SHOULD BE TAUGHT in school to give future researches a base.
Contrary to popular belief (because it's taboo in science) there are many scientific (used in the strict sense of the word) studies that show there is something metaphysical in the human mind occurs and can affect the world around.