Why do the Council block websites from schools?

There are many times at my school when students are unable to get onto certain websites that have been block by our local council, "Kent County Council." I have done some research and found out why this is done:
The council claims that they block websites to ensure appropriate, effective and safe use of electronic communications.
Furthermore they say that pupils are ahead of them with social networking, instant messaging, text and mobiles, they believe this could result in young people having a lack of appreciation of online dangers and the consequences of their actions. They recognise online bullying and want to block any sites that could encourage this behaviour, for exapmle MSN, Bebo etc . There aim is to protect children from the dangers of the internet, CEOP.
Moreover, the council state that schools have to have this policy to protect themselves from legal challenge. The council provides schools with this E-Policy to protect them, otherwise laws could be broke having children misusing the internet, (uploading abuse, inapprotriate images etc.) Schools not only are protecting their students but themselves they have to follow the
Computer Misuse Act 1990.
Though the council doesnt dicourage the use of the internet they believe that the internet is a very important part of students lives but the E-Policy is there to minimise dangers of the internet.