Oml, okay. So. Chara isnt evil. YOU are evil. You're making Chara kill everyone. Charas determination is in frisk, because Chara was buried below the flowers they fall on. So Chara is basically in Frisks body. When Chara asks you if you would like to erase the world with them, and you say no, all Chara knows now is to kill because YOU taught them to, so they feel betrayed and erases the world without you. So, in conclusion, YOU are evil if you pick genocide, not Chara.