Also I'm gonna add that Chara's not exactly 100% evil here. They have a valid strategy! Defend yourself if someone's trying to kill you. Or in the words of Malcolm Reynolds: "Someone ever tries to kill you, you try to kill 'em right back!
I mean, yes the monsters can be nice if you befriend them, but in Chara's case (thus far) I think they just want Frisk to live. That and they're hoping to see their Father. But we'll have to see how this all pans out to be sure.
Really is sad about Metta though.