I understand what you mean. I don't like Jiwook but the rape incident with his brother almost anybody would do what he did (not all) having someone take their place for their "punishment" happens more often then you think. I'm neither saying that what he did was right he just did want any logical person would do.
what^
It was certainly not normal. Jiwook wasn't reacting. Jiwook is the one who set things into motion. He deliberately set Siwon up to take the fall for him. He took advantage of Siwon's desire to help him and used him, knowing full well that Joohoon would wreck his brother.
To me, it seemed like Siwon only wanted to tell those guys to back off. He never knew he would be raped or "punished." He looked very shocked.
The reason I hate Jiwook so much is that he knew what was coming. He wanted to hurt his brother. Before he plays the helpless brother act, asking Siwon "you can help me?" His mind remembers "be a cunning fox" crap. I would never do that to my sibling.
He knew it was coming because it was supposed to be him because that is what Joohoon (I think) said. I could've been misreading
I get feeling bad for Jiwook bc he has mental issues but actually liking him? He let his brother get RAPED. Like idk why anyone would like Jiwook when the real Siwon is dead because of him. The real Siwon deserves justice like wtf