Students could also chew gum obnoxiously. This distracts the class and the teacher. People say that chewing gum can help you focus more, but it can also be the opposite. Students could be paying more attention to gum then the teacher/work.
I understand your point there, but really, it's not hurting anyone. When a student chews gum, they can either throw it away, or stick it under their desk. Just because some students put it under their desk doesn't mean the entire class should get punished. Gum also helps with digestion. Go figure. Like I said again, it helps people stay calm during tests and helps the mind.
I'll have to disagree with you there. Sticking gum under your desk is not fine at all. The custodians or the teachers will have to pick it up. And be honest, would you want to pick up gum on someone's desk? Probably not. I also never said that it is hurting anyone. It is just annoying hearing a person next to you obnoxiously chew gum. They probably spit on you accidentally in the process. For these reasons and evidence, I think chewing gum shouldn't be allowed in school.