If we see only light, or only dark, there is no juxtaposition, no comparison of action.  One day it will be possible to transform those who hate into those who love, but are we there yet?  Is the world not showing us the way right now?  She's saying, "Here my little children is what war looks like, here is what evil looks like, here is what grieving looks like, here is what it does.  How will you respond?"