I think, and that's my personal opinion, that Levi is in a state where he doesn't think he can depend on others. He's too traumatized, when Isabel and Farlan asked him to trust and let them do their thing, they died awful deaths.
His struggle is purely emotional. He's lost, he doesn't know how to proceed, how to reach out to others because he's afraid, anon.
He's emotionally weak. He doesn't control himself, he relies on physical violence and insults because he doesn't know any better, but he tries. He's fucking autistic and I love it.
He was brought into this lifestyle fairly recently and he's known nothing but deaths after deaths. The only person who he's got left is Hanji and that's really fucking sad. He's either even more damaged now or low enough to start the fucking change he needs.
So in other words, he's basically a prisoner of his own fears when it comes to human relationships. He can learn though, as long as he's got the right people beside him but since he lost Erwin, who was the person who gave him a purpose in a completely no homo way, it might be even more difficult, but possible still.
The more recent smartpass said something fucking important. Levi knows the situation is shit, but he still wants to believe in something and despertaly so. There's a chance for him to grow.>But Levi is a fucking monster that has no qualms killing people.
You don't have to like him, but he's got many sides. He's the hero everyone looks up to who will threaten a young girl with violence because he chose that hell over humanity dying as a whole. He, just like Rorschach, doesn't care what's right or wrong as long as the end is worth it. Moral absolutism.>I don't think anything justifies sadism.
Levi doesn't get any pleasure from it. He has sait it himself, he's playing a role that he would avoid if he had the chance.