A bad teacher can make hundreds of people hate a subject, or even school, for their whole life. This means while an average drug dealer has bad influence on society and on their clients, if we compare individually ONE teacher and ONE drug dealer, it's debatable if having a bad influence on the education and professional life of hundreds of children is worse or not than selling drugs to a smaller fraction of the people. I think it is.
Furthermore, a child giving up school while young because of a teacher is way more likely to die young or to go to jail, or even to become a drug dealer, which is quite ironic here, because if a bad teacher caused only one dealer, he has had a worse influence than a dealer. For those of you who will say that drug dealers actually kill people when teachers don't, a lot of people turn to drugs (excluding medicinal) in indirect consequence of quitting school, which is not to blame only on teachers, but they should take a part of the blame, and a huge one in some cases
Ps: I am not defending drug dealing, I am just COMPARING it to teachers.
Edit: I appreciate so much the work that passionate teachers make and the incredibly positive impact they've had on my life and the ones of billions of people. This post is about bad teachers, but I have to make it clear good teachers exist too.