Idk he was sorta right to say those things, he loves his sister even though they argue allot, wouldn't you be angry if someone said something trashy about someone you love? Would you just stand there? （｀ー´）
I (unfortunately) have a brother who's as self-destructive as Inha (broke my guitar, xbox, stole my things to sell among other things). I already reached the point where I cut him off from my life. Sticking with such negativity and clinging to hopes only drags you down. I believe Inho makes it worse by putting down Inha's dreams all the time in the name of support. Of course that would only make her act worse. So, yeah, I would just stand there. He's obviously the person to not stand there, but he didn't even get to graduate high school because of it. If he had just listened to Jung and spent that moment running the action through his head first, instead of running head first-
It really looks like Inho brought this upon himself, making enemies left and right. Jung tried to stop him several times.