The bold sentence is exactly 100% of the reason intelligent design does not belong in a science course. There is no problem teaching it in theology or philosophy classes.
If non-science is put into our science courses, children may because confused about what "science" means. It seems that even many adults do not understand what differentiates science from the arts or theology, a sad state of affairs. The things taught in science classes are pieces of information acquired through application of the scientific method, and that's the way it should stay.
You statement is the statement of someone who has not looked at ID carefully and thoroughly, but is content to regurgitate the half-baked contentions that other shallow thinkers have made based on their own limited study or hearsay evidence.
Yes, we've had more than enough confusion of our children in other areas like history, political science and economics. Your point is well-taken.