I understand the libertarian position that the state should not be involved in the planned taking of life (with some notable exceptions for law enforcement action and the narrow places where libertarians can justify military action) but this is an outrage and an affront to human dignity.
If there were ever a poster-child for the application of the death penalty (as is explicitly allowed by the Constitution) it is Anders Breivik, the Norwegian mass murderer and terrorist who killed 77 people last year. In my estimation, it's not a question of when he should be eradicated from society but how.
I would prefer that his neck be publicly stretched or that, at the very minimum, he face a firing squad. At least the punishment would fit the crime.
I won't ask you to justify the post-modern insanity of sentencing this looney toon to just 21 years, but if he were in this country, I would ask you this: How could we justify not executing him? How about James Holmes?