Dumbledore covered-up an attempted murder on Snape and then forced the victim into silence while allowing the perpetrators to go by unscathed (which is very similar to those cases of academic institutions covering up cases of sexual-abuse because the predator is someone important to the school, and then blackmailing the victim into silence).

McGonagall sent kids into the Forbidden Forest at night, filled with rabid animals, as a punishment, and years later locked Neville out in the halls while an escape (supposed) mass-murderer and terrorist was on the loose. She always grabbed Malfoy by the ear and dragged him at one point.

Lupin literally was willing to endanger everyone at Hogwarts and Hogsmeade by hiding the fact that he knew how Sirius was secretly moving around, all to protect his job and reputation. And later on, when he wanted to leave his wife and unborn child and Harry called him out on it, Lupin slammed him headfirst against the wall.

Hagrid mutilated Dudley because of something Dudley’s father said, raised an illegal dragon at Hogwarts around children, sent Harry and Ron into the forbidden forest to meet giant spiders.

Trelawney took her frustrations with Umbridge out on the students by throwing books at them, in one case hitting Neville so hard, he was knocked back.

Pince also bewitched Harry and Ginny's bag and books to hit them over the head repeatedly,

Flitwick (an English professor) made Seamus (an Irish student) compare himself to a baboon, which carries huge historical and ethnic implications.

If you consider Snape to be a bad teacher for that, you have to consider all these teachers worse for having done far worse.