Get rid of the bad students (and the notion that they're entitled to an education), make the schools safer, and there will be more interest in teaching.
1) Getting rid of "bad students" without any consideration to why they are "bad" will do nothing to stop the actual problem you speak of..namely them being "hoodlums who don't want to learn." Nothing good comes from treating any segment of society as of less worth then any other.
2) Students will only take education as seriously as it is instilled in them that it is serious. While this task certianly rest on the parents shoulders above all, inner city schools with little resources to go by and teacher that enter the situation feeling, much like you do, that these "bad" kids are just dangerous and incapable of learning, it's pretty easy to just give up on yourself as well.
3) I know teachers. They get by. But barely, esp. in the city where standards of living are higher and the best teachers are NEEDED. And frankly, with salaries anything less then better that comperable careers within the same disciple, there is no insentive to become a teacher. Even with a good classroom it is still an very deficult, mentally and phycially taxing job that most people CAN'T do well.