If you live in the UK I am surprised that you are not aware that the recent unprecedented levels of migration have become a main stream issue for all the political parties, but this thread is not the place to discuss it.
Breivik committed an inconceivably horrific act of mass murder, as others have before him.
Each were driven by some issue or other.
Rational concern and debate about serious issues has nothing to do with an individual going bezerk because he supported one side or the other, and they should never become part of the debate.