Loki is an interesting character. In one of my books (The Children of Odin: The Book of Northern Myths), he is always referred to in the first third of the book as “Loki, Doer of Good and Doer of Evil”, indicating that he never plans to do good or evil; they result from his actions whether he wants them to or not.
He never strikes me as TRULY evil at heart.
Even when his actions resulted in the death of Baldr, I think Loki might have done it simply to see how Baldr reacted to experiencing pain for the very first time (not anticipating that tiny amount of mistletoe would be enough to kill Baldr), which would fit his character as the God of Mischief. He pulls pranks on and trolls his fellows, but he’s not the type to attempt to deliberately murder someone.
When Frigga tried to get everything to weep for Baldr so Hel would release him, Loki took the form of a Jotunn and refused to weep, just to see what would happen. What results is Baldr being forced to stay dead until the Ragnarok, and Frigga (quite understandably) loses her trademark cool and she banishes him to torment in Hel forever (although I’ve read versions where Odin made the banishment decree as well). But Loki still didn’t MEAN to ruin everything or destroy anybody’s world; he’s simply a pathological prankster, and literally cannot help or stop himself when he sees an opportunity to make mischief.
For instance, the only reason he aided Thor in retrieving his Hammer from the giant Thrym was because he knew what it would mean for Asgard if the Hammer remained lost, and (more importantly) the opportunity to (endlessly) mock Thor wearing Freyja’s dress and having to pretend to marry Thrym meant that Loki would be provided with many opportunities for less catastrophic mischief later on. Even for Loki, the end of the world is no joke.
He’s less evil and more suffering a total lack of any sort of impulse control, which brings about evil results, and the death of Baldr was simply the joke that finally crossed the line.
Of course, after he’s had poison dripped in his eyes in Helheim for thousands of years, he’d be understandably a bit vindictive and cross, and becomes less about mischief and more about vengeance, which is a key event in the start of Ragnarok.