I think that may be the issue. Arya and Robert are likable. And we want the people we like, who seem good, to be good. There are villains like Jaime who are evil and we like him anyway, though more people are trying to make him good now that he is more likable. Cersei and Theon, in my opinion, were never lieable so it is easy to put them in the evil catagory and leave them there. Robert was kind of a weenie evil guy.