There's a number of reasons for this but most of them flow from the fact that education in this country is run by people who don't believe aims and values ever collide, that no trade-offs ever have to be made.
They are wrong. Take one problem which will affect the delivery of education at all levels. There may well be social integration benefits from having kids whose reading ages can vary from seven to fifteen in the one class, but the educational benefits are less obvious, to put it mildly.
For mixed-ability to work, you need smaller classes. Clearly the government is unwilling to pay for them, so classes need to be streamed. But the idea that schools can serve both the social integration and educational function the government wants them to is an illusion that stems from the belief that compromises never have to be made.
It's the same with discipline. There may well be benefits from more socially-liberal schools but people should stop pretending that there has been no cost to this. Take uniform. It's simply a mechanism of social control and a means by which the teacher can present him or herself as an administer of the rules. It's not the be all and end all, there are other mechanisms but if all of them are to be de-legitimized, people shouldn't be surprised if the medicalisation of social problems and the presence of police officers on school campuses becomes an even more prevalent feature of our educational landscape than it is already.
My own view is that a liberal education properly understood should deliver the pupil from the tyranny of the here and now and has nothing much to do with allowing them to 'do their own thing'. This stands in contrast to the socially-liberal model, which sees schools more as rights-vindication centres and which eschews attempts to impose order as 'oppressive'. But those well-meaning lefties who have advocated this for so long and who dominate teacher-training colleges have to understand what they have wrought. We now have fewer schools with uniforms but many more with metal-detectors. If people think this is an improvement on the past they should say so. But they should stop deluding themselves that the two have nothing to do with each other.
Update: Just had a text from a friend and former colleague who is very upset because her eleven-year-old nephew has been assaulted by some older boys when he was at a Secondary school in Ayrshire visiting from the local Primary.
It was a nice induction day - he was kicked unconscious.
The boys, despite having been previously disciplined for bullying, were only suspended for three days. Three days suspension during the fag-end of a summer term!
This would be an example of the policy known as "social inclusion".