Board Thread:General Discussion/@comment-5102537-20140620091030/@comment-5674726-20140704183226

Kilgharrah was able to blackmail Merlin into making a vow to free him. He did not have the power to force Merlin to keep his vow and Merlin knew this. I should also point out that, while Merlin committed to freeing Kilgharrah, he made no promises about when he would do this. It was therefore open to him to wait until Uther died, or until Kilgharrah vowed not to attack Camelot, before releasing him.

As for Merlin thinking that Kilgharrah wouldn't attack Camelot if he freed him, I'm afraid that the only way I could see that happening is if he was so stupid that everybody who ever called him an idiot was overestimating his intelligence. Not only had he seen a vision of Kilgharrah attacking Camelot, when he asked him to promise not to harm Camelot, he refused to do so. Merlin still chose to free him, even when he knew that it would mean the deaths of hundreds of innocent people. He has Guinevere to thank for the fact that Arthur wasn't among the casualties.

At no point was Merlin ever held accountable for this but, as the troper pointed out, the storyline would have been treated very differently if one of the "villains" had done the same thing.

Imagine if Morgana was the one to unleash a monster on Camelot as a consequence of saving Morgause's life, ie. if the ritual performed on the Isle of the Blessed was one to heal her sister with the release of the Dorocha as a side effect. Even if she hadn't known what would happen - something that cannot be said of Merlin - I can't see it being treated as anything other than a horrific crime on her part, or that her desire to save the life of a loved one would be viewed as any kind of justification for her actions. It's also a safe bet that she wouldn't have been "rewarded" for her actions by having Morgause live; I would lay odds that the newly healed Morgause would have been killed by other means before the end of the two-parter.