Teachers should be able to carry some form of weapon, Just never use it. Some pupils have no respect towards teachers and the teachers having to stop the lesson to check someone's behaviour, It puts the rest of the class's education in jeopardy so a little fear wouldn't hurt anyone.
It is dangerous and the students might get scared. Also, what if the teacher isn't reliable with a weapon? They might use it for bad stuff. For example, school shooting. Also, what if the teacher doesn't know how how to use the weapon? What will they do in an emergency?