I don’t see a problem in mentioning ID in school, as long as it’s only mentioned and not actually endorsed and taught. Something along the line of, “There are ideas other than the Theory of Evolution, however. For example, the concept of Intelligent Design is. . .” (and I have no idea really what the concept of ID is exactly, so I can’t finish that sentence). Letting students know what a lot of other people in their society believe in is a good idea, just so they’ll be able to interact with those people more easily.
As for whether faith is a good or bad thing, that’s not an absolute. It can be either, or even both. There are many people out there who are happier and more productive than they used to be because they “found Jesus” or gained some other faith. Even if they are deluding themselves, so what? They’re satisfied and I’m happy for them. And many religions have some excellent ideas on ethical codes; just think of how much nicer the world would be if more people took “Therefore all things whatsoever ye would that men should do to you, do ye even so to them” to heart? Or faith can be a bad thing, such as if somebody decides to use you as the latest sacrifice to their gods. Overall, I don’t really care what other people have faith in, as long as they’re polite about it. If somebody wants to stand on a streetcorner and hand out fliers about their religion, that’s fine. I might even listen to them, because they sometimes have things to say worth hearing. It’s when people try to make me have the same faith as they do that I get annoyed.