I don’t understand people who want to view or label Loki as this black and white, one dimensional villain, when it was plain as day to me from the first time I saw Thor 1 that he was far more complex and played far more of an ambiguous role than that.
If you really pay close attention to everything Loki does from the very beginning of the first film, to the end, it’s all motivated by actual good intentions. I know that some might have a difficult time realizing this, as it isn’t explicitly stated and shoved down their throats, which is the only way some people seem to be able to actually receive a message. Loki’s methods are definitely questionable, but I think what people need to understand about him too is that, we’re never given to believe Loki was ever mentally fully healthy. He’s plainly an emotionally and mentally unstable young man from the start, and by unstable, I mean when we meet him he’s a person who’s been led, intentionally or not, into believing that he isn’t as loved as Thor, that nobody really likes or respects him, who perceives himself to be regarded as lesser, and a lot of that belief of his is based on the actual treatment he receives. He isn’t delusional, but his perception has been warped through, in one form or another, a kind of abuse.
Observe the way he’s treated by Heimdall, who tries to KILL him simply for upholding Odin’s decree on Thor’s banishment, tries to MURDER Loki when he confronts Hiemdall over committing TREASON regarding, not only Odin’s, but his own decree, as king regent, by letting Sif and the Warriors 3 go to Midgard to bring Thor back. Heimdall literally tries to chop Loki’s head off for this. And then there’s Sif and the Warriors 3, who make open fun of him and accuse him of being a coward, accuse him of being the architect of Thor’s banishment without any proof whatsoever, and, without apparent qualm, plan on dismissing Loki’s standing as king regent by completely disobeying his orders that they aren’t to go to Midgard to bring Thor back. Again, just like Heimdall, an act of legitimate treason. And even Thor mistreats Loki, talking over him like his opinion doesn’t matter and telling him essentially to stay in his “place” when he tries to talk Thor out of going on a murderous rampage.
Look at ALL of this if you need proof that Loki isn’t respected, by right of his social status within an autocratic system, as he should be. Look at all of that, and you’ll understand why Loki thought that he obviously needed to do something extreme to earn any love and respect, and why he thought he needed to do something extreme to get Odin’s attention. He KNOWS Thor isn’t ready for the throne, even as Odin remains ambivalent about it, but is going ahead with giving it to him anyway, and so Loki surmises that he’s going to have to prove to Odin that he’s making a grave mistake. Which, consequently, he DOES prove, because Thor goes from 0 to a million in about 0.01 seconds, wanting to invade Jotuneheim and start a war over the actions of a few Frost Giants. He then proceeds to actually go to Jotunheim and slaughter who knows how many Frost Giants, because one of them called him a “princess”, despite Loki’s very much real and desperate attempts to get him to calm down and go home. Now you might argue, ‘But Loki’s the one that goaded Thor into going into Jotunheim in the first place!’, and yeah, that’s true. But intention is always important when evaluating someone’s actions, and Loki NEVER intended for Thor to make it to Jotunheim. He wanted Odin to catch Thor trying to go there so that he would then see that Thor wasn’t ready to assume the role of King. That was Loki’s SOLE intention with the entire affair. Things of course got drastically out of hand and the rest of the film’s consequences play out from that. But Loki was, at the root of it all, trying to do what he thought was right for his Realm, for his brother, for his father, and for all of them. He knew Thor was reckless, knew he was consumed by a lust for blood and battle, and that he didn’t yet possess the wisdom or maturity to make a good, or even passable king. He knew Thor on the throne would be an unmitigated disaster, and so he went about preventing it the only way he knew how.
And let’s think about how Loki does go about that for a moment. He uses manipulation, trickery and deceit. Why? Well, if we take a look again at the way others regard Loki in this film, constantly cutting him off, making jokes at his expense, talking about him like he’s a coward and a liar and about how he’s “always been jealous of Thor”, do you think, if Loki actually appealed to any of these people forthrightly, and told them his opinion about Thor taking on the throne, that they would even deign to listen to him for a moment? It sure doesn’t seem like it to me. And Odin’s shown to be an extremely stubborn and willful personality, who when he’s set his mind to something, won’t be dissuaded by anybody (ala, Loki trying to intervene when Odin is banishing Thor, and Odin literally growing at him like a wild animal to shut him up). From all of this I think we can justifiably assume that Loki probably felt there WAS no other way for him to make others listen to him about Thor then to simply SHOW them how reckless and selfish Thor actually was. Everyone just acted like the sun shown out of Thor’s ass, and Loki was just a jealous, meddling, unlikable coward by comparison.
From there things only become more tragic and complex. Loki finds out he’s a Jotun. Not only a Jotun, but a Jotun runt, abandoned by his real father to die alone in the cold. He finds out he’s a part of a race of beings who have been, since as far back as he can remember, regarded as the mortal enemies of the Aesir. Regarded as literal monsters. He finds out he’s not really even an Aesir, he finds out he’s not really Odin’s son, or Frigga’s son, or Thor’s brother. He finds out he’s, according to the culture he’s grown up with for over a thousand years, an abomination. All of this converges with Loki’s ever increasing feelings of being less loved, less wanted, less worthy, just lesser in general, than Thor in not just Asgard’s eyes, but in the eyes of his parents, and boom, you have the perfect mixture for a serious, massive, world shattering crisis of self identity, and Loki, who as I’ve pointed out was already standing on a precarious edge of mental health, has a mental break and snaps. He becomes so distraught and so desperate to PROVE that he isn’t a monster, that he isn’t evil, that he isn’t unworthy of love, that his teetering and devastated mind concocts a plan to prove to Odin that he, in his own words, is a worthy son, that he’s every bit as much an Asgardian as Thor, that he’s as loyal to Odin’s house as Thor, maybe even more so, and in his breaking mind, he concludes that the best way to do that is to destroy the very race of monsters from which he comes, thus severing any and all ties he has to Jotunheim and solidifying his ties and loyalty to Asgard. Loki’s a hurt, and mentally ill unit, which people don’t seem to take into account when assessing his actions. Thor has no such excuses. Thor’s a perfectly healthy young man, with a healthy sense of self esteem and pride. He knows he’s loved by his family and his people, and he knows he’s destined for greatness, and yet still he goes on murdering rampages and seeks to kill, not for any reason beyond the thrill of it. Loki knows no such thing at all about himself. All he knows is that people dislike him, they don’t trust him, they think he’s a coward, and that Odin chose Thor over him to be King, despite his own doubts and hesitations on that front.
Loki doesn’t try to destroy Jotunheim because he’s got blood lust. He tries to destroy Jotunheim because he’s convinced it’s the only way for him to prove he’s NOT a monster. It’s completely tragic, and heartbreaking, and not really the actions of a villain at all, more the actions of a mentally and emotionally broken young man with probably epically low self-esteem because everyone’s always treated him more like he’s a barely tolerable stain on the shiny greatness of Asgard than it’s actual fucking prince.