User blog comment:Morganaforever/Morgana's reasons/@comment-5995315-20130213225350

Gwen is the one person in Camelot for whom Morgana bore no real hatred.

Uther and Arthur are the only ones for whom she bore any real hatred.

Whether she hated the others depended only on whether they got in her way.

Hatred can have a rational basis, but it becomes irrational if its outcome makes no sense. Morgana's hatred of Uther is understandable and its outcome made sense.

Arthur is different. With him, Morgana's hatred became all-consuming and its outcome makes no apparent sense. But Morgana became psychotic as the story went on, so in her mind her hatred remained rational.

If you could have asked her at the end whether it was worth her life to kill Arthur, she would have said yes. Whether that's rational depends on whether you're Morgana or someone else.