Sure, you can like whatever character you feel into. But, you can’t convince anyone when you say he/she is a good person. You know very well that’s not the truth, if the said character is a killer, a psychopath, or/and a rapist etc. Sorry, that’s what I think
I can’t stand Eunseo either but people gotta realise she‘s mentally ill, just like Sangwoo. We don’t know why she’s like that, we don’t know if she was abused as a child. While that doesn’t excuse what she did to Sangwoo, I don’t get how people can love Sangwoo, who kills people, and be completely apologetic when it comes to him, but hate Eunseo like she’s the devil without considering she might have a painful backstory too.
Sangwoo and his mother are not as different as you’d like them to be.