I'll probably later regret getting into this, but it's Molag Bal's desire to corrupt and enslave that makes him seen as evil. Yes, Tiber Septim was a prime example of the Dragon's and Dragonborn's drive to dominate others, but unlike Alduin, he didn't brutally enslave or oppress those whom he gained power over. His empire, in fact, banned the practice of enslaving others. Yes, some of them do seem to have alien moralities, but some are less alien than others.
It could be argued that Sheogorath and Peryite also corrupt, but they view madness and disease, respectively, not as curses, but as blessings. Molag Bal, on the other hand, seems to be much more insistent that he's not trying to do anything that he'd consider "good" even if we are going by the idea that he may think of it differently than mortals. He's not trying to make some philosophical statement of how horrible the world is, he's not trying to give people his idea of "help". Whatever his own idea of morality is, it can be classified in mortal terms as "evil". In fact, I imagine most beings that would be considered evil didn't consider themselves to be evil.
Which is why I made this thread. I want you to class them according to YOUR point of view. Morality is highly subjective and something good for someone, might be considered evil for the other. I want your input on the matter. I want to know where most people would categorize the Princes according to their actions. I don't want to put an objective definition to good and evil, in most cases(but not all), it's entirely subjective. If you don't want to put them under any category or if you don't have an opinion on the matter, that's fine. I'm not here to discuss whether your view of good and evil is wrong or right. Mostly there are two things that matter. Your opinion, and the general opinion. IE: What is considered good and evil by your standards and by people's standards according to you.
In TES it's good because it's either freeing the soul from the material prison or freeing the soul from a middle-class body to reincarnate as something potentially better.
Well, then, do you consider the deed Azura made you perform good or evil?