While it could be interpreted that he wanted to protect Thor from what he saw as certain death from Hela, Loki still acted against his brothers wishes and wanted to take his choice away from him.

In Thor: Ragnarok, it's revealed that Hela is Thor and Loki's long-lost sister, a Goddess of Death who helped Odin conquer the nine realms making up Asgard. Upon her return, Hela points out Odin's ...