This isn't about the kids who put the occasional toe out of line. It's about the kids who, lesson after lesson, day after day, take up between 25 and 50% of classroom time to manage to the detriment of the much larger number of students who could do much better if only I had more time to dedicate to them.
I get @Florenz 's point on that. We have a system in my school which has us give kids 5 chances before they need to leave the classroom. That's 5 interruptions per student. Say, in a class of 25, you have 3 students who persistently disrupt, that could be 15 times you have to stop and deal with those 3 students. Include giving them the necessary time to change their behaviour, that can easily be 15min of time gone. Every lesson. An hour a week (4 lessons a week in a core subject), that's a full lesson every week gone due to behaviour of 3 students in one class. The other 22 children have to put up with this.
I have a lovely class of 15 who include 5 children who simply don't want to engage. The 5 frequently come in late, talk over me, swear at me a bit and then walk out, having taken up around 15-20min of lesson time to do so. They do this every lesson in every subject. The nice students who want to learn have simply accepted this now. I quote "Miss, that's just how it is". There are no consequences. I feel for the lovely kids in that class and I equally feel sorry for myself, having to put up with the disrespect every lesson.
This is not even touching on the more serious behaviours. A kid throwing furniture at me while I was pregnant, who was back in my class after 3 days of exclusion and I was still expected to positively engage with the child who had threatened the life of my unborn baby. Not uncommon in schools now, either.
But those are the kids that grind teachers down. And others around them. In an ideal world, should we write those kids off? Of course not! But if they stay in classrooms as currently happens they have a very real detrimental effect on everyone else, and whose needs should trump in that situation? That of a handful of very disturbed children from a bad background or the rights to education of the many others whose education gets disrupted, day after day? Or even, heaven forbid, the right of teachers to NOT be abused in their workplace day after day?