User blog comment:MerlinUSA/Lies My Dragon Told Me/@comment-5577678-20130129184358/@comment-5674726-20130131000435

''When a show deals with a fate of someone that can't be changed it should stick to it instead of changing it all the time. Merlin's future was either written since the dawn of time, as the Villia said, or it wasn't.''

Given how things worked out, I'd say that the future where Arthur and Merlin are a fantastic team who unite Albion, restore magic, turn the place into a Utopia, etc, was just one possible future among many, and that Kilgharrah either believed that this one possibility was a destiny set in stone or was doing his utmost to bring it about. Perhaps Morgana becoming an enemy of Arthur and Merlin's was a key component to bringing about the future he wanted, if the kingdoms of Albion were supposed to unite under Arthur's leadership to defeat a common enemy.