People stopped seeing Palestinians as people. It's easier to defend the actions of the IDF if you don't have to see the faces of the children they kill.
Saly was a child. She was not a terrorist, or a 'regrettable but unavoidable casualty', or 'collateral damage'. She was a child.
When people rush to support the killing of innocent people, perhaps they should instead think that Saly was a little girl with hopes and dreams, so similar to all our children. So are all the other children alive and dead in Palestine today.
There were alternatives to this. But this course of action, this mass killing of innocent children, this was what people chose.