Firstly, Merlin wants to save everyone whether s/he is friend or foe. It seems like a way to extend the story. Merlin kills pixie/ sidhe etc creatures without a second thought but saves Uther/Morgana! Kind of a mythical racist.
Uther banding sorcery, he also thinks it barely exists.
Almost in every episode there is at least one close shot of Morgana's evil grinning which is too obvious to show and weird of others not noticing. She goes out every night and no body sees her! There is no guard either!
(NB: This is my second post. Sorry if I'm repeating something. Thanks.)