Last year the school I intern-taught at had a bullying prevention in-service. One of the things I learned was that quite a few bullies go into education in their adult lives (I can't remember the different percentages).
A lot of teachers talk about respect being one of their first rules - for students to respect themselves, the teacher, and others, and for the teacher to respect students. It sounds like those teachers didn't necessarily feel that rule had a place in their classrooms - or that they felt as teachers, they did not need to follow it.

This is really disturbing, and I fear that it happens a lot more frequently than we realize. I wish there were better systems in place to make teachers more accountable for this type of thing. I had a teacher growing up that made fun of the students who struggled to learn, and naturally, the other students followed her example and made fun of the struggling students along with her. I have a friend who also had a teacher that you could say encouraged bullying against him as a child. My friend is very gifted in both art and science and was always much smarter than his classmates. For one project in school he did a presentation on computers which no one in the class (including the teacher) could understand, because the concepts he was presenting were so complex. At the end of the presentation the teacher simply said "no one can understand a thing you're saying, and put your fly up for god's sake". The students, naturally laughed hysterically at him and it lead to consistant bullying. Now he's 32 years old and has battled depression his whole adult life, and he'll probably never be able to get off of his medication. It's an extreme example, but a true story of what this type of insensitive behaviour by teachers can lead to.

The downside of Minnesota's strong teachers unions are that it's almost impossible to fire even really bad teachers.