User blog comment:Morgana High Priestess/Could have Morgause brainwashed Morgana?/@comment-5674726-20130311001301

It's definitely an intriguing possibility, and it's one that I'd have liked to see the show explore but I doubt it's something that the writers ever seriously considered using.

Imagine the implications if they had.

When Guinevere was held captive by an enemy magic user for a few days and exhibited changed behaviour after her return, they gave her the benefit of the doubt, recognised that she wasn't responsible for her actions and sought to free her from the enchantment. When Morgana was abducted by an enemy magic user, spent more than a year away, returned with a very implausible story about where she'd been and exhibited changed behaviour after her return, the idea that she wasn't acting of her own accord was never considered. Even before she returned, Gaius erroneously claimed that she chose to use her powers for evil.

Had they revealed towards the end of Season Five that Morgana had actually been enchanted since Morgause spirited her away after Merlin poisoned her, it'd be difficult to ignore the thought that, had she been given the benefit of the doubt, they might have been able to help her much sooner and thousands of deaths could have been avoided.