Originally Posted by cherokeesam
let me give you the short answer first: Loki is traditionally a villain. Thor is traditionally a hero. Period.
That's what people expect to see --- Loki as a villain. It's great that he's got sympathetic qualities (or at least started with them --- he seems to have lost them by the time Avengers begins), but he is a villain; so *nobody* is expecting to see him turn into a hero. Ever. Might as well expect to see Joker turn into a good guy.
However the Joker did not have the characterization framework that was set in place for Loki in Thor 1. So there is a BIG difference between those characters there. With a character set up like that, anything can happen, all bets are off.
And, being someone who saw Return of the Jedi, in theaters when it was first released. I can tell you that I and I'm sure most people NEVER expected Darth Vader to do what he did. (and I read a lot of Star Wars comics in between films)
And as for comparing Thor's and Loki's motives in slaughtering Frost Giants: Thor's motives are the defense of Asgard and vengeance against Frost Giant incursions. So at least Thor and Odin have "moral superiority" on their side, even if it's debatable. Loki, on the other hand, plotted genocide of the Jotuns *purely* for the reason of making himself look like the greater hero and savior of Asgard. Thor's motive is *selfless* in that he's thinking about the safety of his people; Loki's motive is *selfish* in that he's thinking only about how this will increase his political power.
yes the motives are different, but I would add to Thor's motives a strong desire for blood and war and glory, which does not make him too "morally superior" there. And to Loki I would add the motivation of the shock and horror of just finding out after 1000 years of life that he's one of "the monsters who parents tell their children about at night" and desperately wanting to erase them from existence, in the hopes that, if they no longer exist, it will mean he never has to face *that* reality, or admit it to anyone else. Selfish yes, but not the same as being just about the power, just as Thor's actions are not just about killing all the Jotuns for fun (although again, he certainly looked like he was having fun there!
which is again, not so "morally superior" of him
and I will also add to Loki's motivations there actually, the threat of a war with the Jotuns, which his brother started. As he says to Heimdall as he leaves after visting Laufey "You will open the bifrost to no one, until I have repaired the damage my brother has done" So more motivation here is to stop the Jotuns before they attack Asgard. (not so selfish)
Also, you are forgetting...
Loki: I never wanted the throne, I only wanted to be your equal.
As I've said to jaqua99 I think before about this quote. He is very very angry here, and the jig is up, no need to lie anymore. So this is the truth
and so this is a great deal of his motivation at least up until he actually gets to sit on the throne (where I would agree, it changes to more be about being on the throne for him at that point)