Depends on the teacher. I worked with some bad azz women over my career. They were feared for their ability to create such a loving bond with their kids that they never wanted to disappoint them.
There are MANY homes where the mother is the primary disciplinarian.
You obviously never attended a Catholic school with yardstick weilding Nuns either.
A good teacher or parent has completely failed their children when fear is the only method of discipline.
Most of all, your street wise Behavior Disordered kids are very savvy and know that their teacher can't get physical with them to impose their will.
Most have grown up in a physically and/or sexually abusive home so they are pretty immune to fear. Trying to intimidate those kids via fear only enrages them and places you/your students in dangerous situations.
Ever watched a prisoner take on 5 cops with mace/battle gear/tasers?
Ever watched a rogue driver speed toward cops with guns drawn?
Fear is not a motivator for them.
Those adults were kids in my classroom at one time.
You wouldn't last 5 days in my classroom with your lack of knowledge and training dealing with those kids.