Board Thread:General Discussion/@comment-27907368-20160528162922/@comment-27620479-20160604083311

It can refer to you betraying her, not the kill itself. Because, as far as I know, if you kill her otherwise, even on genocide, she doesn't believe you will fit in.

She calls you out on agression when others are vulnerable. Does it sound familiar? Who wouldn't be vulnerable after losing a biological and an adopted child? And what did Asgore do? Declare war, before a healthy period of grieving was over. He didn't even allow for a chance to properly bury Chara. Toriel had to take their body, to do it herself.

Then, new children arrived. She treated all of them as they were her own. Then they left, and were hunted on Asgore's order (killed personally by Asgore himself). An order (and an act), he knew was against Toriel's wishes.

So, Toriel thinks that, as a literal backstabber, you will fit into a world ruled by a figurative backstabber.