Asriel... did a lot of horrible things. Killed people because he was curious. Killed people simply to see how everyone else would react, if anyone would miss them if they're gone. Killed people because they pissed him off. Killed people because he got bored.

Wiped out his own people to make the Underground his own paradise. Played mind games with them and get a kick out of their self-destruction. He murdered his Frisk again and again because he finally had a new plaything; he punished them for not being Chara, but decided they'd be a good enough replacement... a stranger he didn't feel guilty about killing.

Not having a soul wasn't an excuse. He always had a choice. Always.

Even if he did know the things this Frisk had done, he wouldn't have room to judge. He'd be hurt, yes, but...