So many many wonderful layers to MCU Loki, so much going on in that head of his. Branding him as just selfish, jealous, power hungry or evil is really not the whole story. Aspects of that, of course but that is not a complete picture of the character at all.
To quote Tom, "every villain is a hero in his own mind" and this is especially true of Loki. Loki believes he knows best, and that is a large part of what drives him in these two films. Is it evil to believe that he can lead the Midgardians into an age of peace just as what his father wanted him to do with the Frost Giants? No, of course that's not evil. not at all. If however one goes about it, in a very misguided "the end justifies the means" kind of way, as Loki does, then that's where the evil acts come in. But that driving force of it is not simply power hungry or hateful or evil on it's own, it's sprung from good intention, and a very relatable intention that I believe most of us would have, but then it is acted on in a misguided, wrong, wrong, wrong, way. Much the same way that Thor at the beginning of Thor 1 acts on his intention of protecting Asgard in a very wrong misguided way.
And of course, Loki is not the only one who believes in "the end justifies the means" in the MCU. We have Nick Fury who takes out Coulson's cards from his locker soaks him in his blood and throws them on the table in order to get the Avengers to act together, and the Council who sent that missile off and potentially kill A LOT of people in order to save the rest of the world. But no one would consider those characters "evil" because of it, I don't think. Note this behavior all falls under a theme of "moral sacrifice" which we believe will be a continued theme in Thor 2.
Now, it is a BIG mistake to think that in Loki's speech to Laufey that Loki let the FG's in simply as "a bit of fun". In that scene he is clearly trying to convince Laufey that he is nothing more than a greedy second son trying to be king, and that he wants him to kill Odin (when he really doesn't) in order to lure Laufey in and take him out, both for his own gain, but for the gain of Asgard and the 9 realms (without that threat around anymore). Loki is an excellent liar, and he is lying there to Laufey. I love how people assume Loki is lying when he says something good but then assume he's telling the truth when he says something bad. It's not that cut and dry. He's being a champion poker player there and not showing his true hand in the game. Why did Loki let the FG's in then, you may ask? The answer is he was being a hero for Asgard
in his own mind. He loves Thor, and at that point accepted Thor would be king at some point, but he truly believed that Thor was not ready, no matter what father said. And so for the good of Asgard he creates this distraction, to push the coronation back more, and he'd probably done all he could to drag it out prior to that too, for the same reason.
THOR
(re: the empty hall)
This was to be my day of triumph.
LOKI
It will come. In time.
LOKI
And if I do, then what? I love
Thor more dearly than any of you,
but you know what he is. He's
arrogant. He's reckless. He's
dangerous. You saw how he was
today. Is that what Asgard needs
from its King?
The others exchange glances, torn. Loki has a point.
So again, he's letting the Frost Giants in as a distraction to put off Thor's coronation here, because Thor was clearly not ready for the responsibility. And ironically, unknowingly, he's screwed himself out of his own kingdom in the future with that act. 2 warriors died, it was certainly not a good thing to do, but the intention did not come out of selfishness, jealousy, or evil. It came from wanting what's best for Asgard and believing he knows best. I believe Loki's love of Asgard is a theme in the comics as well.
Loki: I remember a shadow, living in the shade of your greatness. I remember you tossing me into an abyss. I who was and should be king!
Thor: So you take the world I love as recompense for your imagined slights? No, the earth is under my protection, Loki.
[Loki laughs]
Loki: And you're doing a marvelous job with that. The humans slaughter each other in droves, while you idly threat. I mean to rule them. And why should I not...
Thor: You think yourself above them.
Loki: Well, yes.
Thor: Then you miss the truth of ruling, brother. A throne would suit you ill.
Much the same happens in Avengers actually. Those speeches (and the way he delivers them, very importantly!) where he says "freedom is lie's great lie, and once you accept that you will know peace" and the majority of the speech in Germany, and his chiding of Thor and what a marvelous job he's done with Midgard, citing how they "slaughter each other in droves". He believes he is above them, and he will bring them peace, and he believes he will do a hell of a lot better job than his brother has done. That intent, in itself, is not evil, not whatsoever. Most everyone wants a world in order and a peace. How he goes about it is what is terribly misguided and wrong. Joss also states as much in the DVD commentary of the Germany scene, that it's messed up to want to be that person, to be "daddy" and make everything better. But that is not selfish or evil in itself. again, it is how he goes about it that is seriously messed up.
Another example, using the bifrost to destroy the frost giants, as I've stated there is more than one reason for this, one certainly being wiping off any evidence that he is what he is, so he doesn't have to accept that part of himself, but also, it is a way of stopping a war that is imminent, with 0 bloodshed for the Asgardians. so this is a way of ending that war quickly and stopping the "monsters" from threatening the 9 realms again, thus keeping the peace. He's a hero in his own mind and the end justifies the means in his mind.
Note: at the end of WWII, the US dropped nuclear bombs on Hiroshima and Nagasaki. Within six days of the second bombing the Japanese surrendered. A LOT of people died, and it seems pretty horribly at that, but WWII was finally over and a further tremendous sacrifice of American lives was avoided. Now, was Harry Truman evil?
Going back to if he wants to be king or what. I think he wants what's best for Asgard, in Thor 1. And he comes to the conclusion that he is what's best, not Thor, and he has to make Father see that any means possible. He wants father's approval and to be the "worthy son". Again, it is not evil in itself to feel this way, but messed up in how he reacts and in the way he goes about trying to get that approval. Then when it all comes crashing in around him, after being so close to having that approval, mother and father's love, his place and purpose in the world, and feeling worthwhile, that is when he snaps and we get that " is it madness?" moment with the tear. Ken actually instructed Tom that he wanted to see something in his brain snap, and it might take him a few takes to get it. (LOL, Ken) But it's basically I think a "how am I the only one who sees, that I am right? Is he calling me mad?" moment... not to mention, partially probably "is it madness for me to want a purpose and place in the world? Is he saying I am so worthless to not deserve that?"
RE: Brother... I believe the times he's throwing out the world "brother" there at Thor in a very bitter painful and/or spiteful way. His heart is broken he is not Thor's brother, not Odin and Frigga's son but a son of a "monster", not truly a son of his beloved Asgard, and his jealousy and anger over everything.
Which is it, Loki?? Does he want to be king or doesn't he? And why? If he doesn't like the Midgardians and thinks himself above them, why on earth would he want to spend so much time with them? And is he in the House of Odin or out?
So what's Loki's deal in the MCU? What is he really after? And will he obtain it in Thor2?
I think he is a god of chaos truly now, he has no place in the world. The place in the world he thought had as a brother and a son was a lie. The purpose that Odin had for him is no longer possible. He is in chaos. In the beginning he is "burdened with glorious purpose", and wanting purpose in life is most certainly not evil and something very relatable, but again, the way he goes about it is completely misguided and wrong.
So I guess I feel the thing that would bring him happiness and calm his now chaotic mind is stability and a purpose in life that makes him feel worthwhile. How they can bring him to that point in future films I don't know but should be interesting.
note: Loki's comics and myth, wife Sigyn, aka "victorious woman" she is the goddess of Fidelity, but also the Goddess of Constancy. If he is Chaos, she is stability and constancy, the quality of being enduring and unchanging. An "odd couple" indeed. But from a fairytale/myth storytelling point of view, it is a very interesting combination. It is too bad so much is missing of their life together in the myths as I feel certain she was meant to be a pretty amazing female symbol. I just hope that if they do bring her in at some point in the mcu, that they do more with her to bring him much needed "constancy" than to have her being an abused and neglected wife or blind Loki fangirl as she sort of seemed to be in the comics. (not always. She has her moments. but she should have been handled a hell of a lot better from the panels I've seen, that is for certain). I'm not holding my breath for her to show up, but just saying. It would be an interesting development.