He even says it. “To ruin my brother’s big day, and to protect the realms from his stupidity a little longer.” And then later; “I never wanted the throne. I only ever wanted to be your equal.”
He knows about Thor’s bloodlust, and calls him arrogant and dangerous when the warriors 3 and Sif wants him to convince Odin to bring Thor back. And he’s right! Thor marched onto another planet and started killing away because he felt slighted. That’s fucking scary, and it amazes me that Loki is the only one to see it.
So yea, originally Loki was actually well intentioned, before he went off the deep end.