That's wrong - they can do that without Lex Breivik. The issue is when he's declared healthy, what would then happen? It's legal to detain him if it can be proved that he constitutes a danger to society. However, if he is not considered a danger to the society, he will be able to walk freely. With Lex Breivik, they will be allowed to detain him as long the society is a danger to the person.

Think about that for a moment. With Lex Breivik, you can be isolated even if you've not done anything illegal (or have finished serving your imprisonment) or is considered healthy, because some people in the society want to do you harm.