.. as long as the subject is taught objectively and unbiasedly, i dont see the harm...
evolution should be taught in a biology class, because it is indeed a science.. it is backed by fossilized proof.. people may argue that it is a theory... yes. it is indeed a theory.. but in science, the word theory is very strong.. a theory is backed by hard facts and is reviewed by numerous people before it can be released as a theory... for example... gravity is still a theory... there are facts that prove it exists.. but theres nothing that completely says gravity exists, because we cant physically see it
creationism is not a theory, however.. its a belief.. it explains things using the bible as a reference point, and not logistical hard facts... it relies more on the supernatural, which is the furthest thing from science.. therefore, it should be taught in a religious studies or philosophy class, and not a science class
either way though, i think its important that these subjects are taught objectively... present their ideas and points to the students.. as long as they arent forced to believe it, i dont see the harm in teaching it.. its always better to clearly know both sides of the fence, before choosing a belief anyway