I used to teach. I did not facilitate healthy debate of differing opinions. That was not my job. I passed on required information and trained students in the skills needed to make use of said information. Facilitating debate and the sharing of ideas is the job of a University lecturer.

Yes, teachers can and do get assaulted, especially by teenage students who don't want to be there. Here in the UK there are no guns, of course, but I've had to deal with knife-wielding students who threatened to cut me if I didn't give them a better mark. It's scary, even if you can handle yourself (and I can). So I can quite see the problem, especially when firearms are added into the equation.