I think this was the biggest problem.
Though he doesn’t discuss it here, we wouldn’t be surprised if Eccleston also wasn’t best pleased about how much of his role in the film was removed during editing. Before The Dark World‘s release, the actor spoke of how he liked exploring Malekith’s damaged psyche and his warped reasoning for wanting to destroy the universe. In the finished piece, however, virtually none of his motivations remained, leaving the villain as a very cardboard character.
I actually thought the character was one of the most interesting villains whose potential wasn’t even touched. Essentially, he was similar to Darkseid in that his actual motivation was a twisted way to end suffering. Darkseid wants the Anti-Life equation because he sees that free will only leads to terrible, destructive decisions, so it would be far better for the universe to have just one will ruling everything… his own. Perfect order.
Malekith had a similar plan. If nothing existed, no one would suffer. Existence is inherently bad, meaningless and no one survives it.