User blog comment:EmrysOfAlbion/Emrys could have been smarter/@comment-4135736-20120503082136

Although it has been really clear that Merlin has lost faith in Morgana, I don't think he wants to kill her because I reckon he feels responsible for how Morgana has become (he did not reveal his magic to Morgana which made her feel alone and rather than tell her the truth that she was the source of the sleeping enchantment, he straight away poisoned her) and if he trys to kill her, it would make him no different to her.