Morgana had a number of reasons:
1) Uther's persecution of those with magic
2) Morgana discovery she had magic
3) Her fear and shame at having magic and being persecuted
4) Morgana's discovery she was Uther's illegitimate child
5) Uther's unwillingness to acknowledge her as his child publicly
6) Morgana's belief that Arthur lacked the talents to be a ruler
7) Morgana's belief that she understood the people of Camelot; later, when that proved to be wrong, her belief shifted limiting her understanding that she represented those with magic; which given the reaction of the Cathar Priest might not be true either.
But in one word: Morgause. Who could have easily ruled Camelot by forcing Arthur to marry her when she bested him in their duel. She was the one who swayed and manipulated Morgana...
1) Uther's persecution of those with magic
2) Morgana discovery she had magic
3) Her fear and shame at having magic and being persecuted
4) Morgana's discovery she was Uther's illegitimate child
5) Uther's unwillingness to acknowledge her as his child publicly
6) Morgana's belief that Arthur lacked the talents to be a ruler
7) Morgana's belief that she understood the people of Camelot; later, when that proved to be wrong, her belief shifted limiting her understanding that she represented those with magic; which given the reaction of the Cathar Priest might not be true either.
But in one word: Morgause. Who could have easily ruled Camelot by forcing Arthur to marry her when she bested him in their duel. She was the one who swayed and manipulated Morgana...
