I don't understand how Aggravaine can't just kill Arthur in his sleep. If Morgana's going to take over anyway it's not like he'll have any consequences for it and I'm pretty sure he can frame someone else pretty easily. I don't fully understand his motives either. Ygraine died, yes, but Uther's dead now and it's not Camelot's fault. It's no one's fault. No one knew it was going to happen.