This is so sad. I do think that many on mn seem to exist is a world where they believe that this couldn't possibly be the case - that their lives are somehow sheltered from this unpalatable truth.
The fact is that a child who has extreme behaviour is still vulnerable, however bad the behaviour is, and whatever the cause (SEN, trauma of some kind, neglect in the home etc). I wonder how many of the poor little souls in the news who have had serious case reviews after their deaths would have fallen into the "naughty for the sheer fun of it" category. Yet when the worst happens, people wring their hands and wail about how appalling it all is, and why didn't others just do more? The same people who are probably the most vociferous about children's behaviour and don't agree that it's a way of communicating some kind of vital information about how a child experiences life, and people.
If parents are not parenting (and I agree that many are not), then I'd like to think we're still a society that should support and protect those children, precisely because they have nobody else to turn to and limited ability to communicate their thoughts and feelings.
Do I think they should be allowed to continue to disrupt classrooms? Of course not. But as a society, we have to do better than simply writing them off entirely, or we've learned nothing since the Victorian age.
The fact is that many children in UK classrooms are enduring neglect, or sexual, physical and emotional abuse, on a regular basis in the home environment. Think about the impact that's having on their developing brains. Just because you live in a nice area, and most of your friends are good parents, it doesn't mean it isn't happening.
The kids i grew up with who were like this either became drop-outs from employment, addicted to drugs or alcohol, in prison, or dead from suicide or disease. But before any of that, they were children. People can say "it wasn't like this in my day/ when I was at school" but memories are selective. They've always been there, but the chances are you've forgotten, because you surrounded yourselves with 'the good kids, from nice homes'. It only becomes apparent again when your own child is impacted by another's behaviour.