This type of enquiry always brings a raft of answers along the lines of - 'Why should Prisoner X have rights, where were the rights of his victims ...'.
That is absolutely understandable, but it is not how the law functions.
In order for law to work to the advantage of a civilised society, it has to put in place its punishments, and then work with them.
In this instance, Mr Breivik's punishment is to lose his liberty - and that brings a raft of problems such as the ones illustrated here.
There has to be a balance struck between Mr Breivik's rights as a prisoner in terms of access to interaction, and his own personal safety given the nature of his crime.
I think, on balance, since interaction with other prisoners would seriously compromise Mr Breivik's safety, and that of other inmates and staff, it is in his own interests that the current level of segregation remains.
It is advised that he does have interaction with prison staff, and in view of the potential reaction of inmates who got within arm's length of his person, Mr Breivik may well be advised to accept that as being the best he is going to get.