The conspiracy theorists on 4chan caught onto a FaceBook glitch that revealed Greta Thunburg's Father and UN's Climate Change delegate Adarsh Prathap posting as Greta. Global, real time spread of knowledge/data/lies/propaganda/slander is now but a mouse click away for everyone on this Big Rock.
Fakebook Facebook, the flaw was quickly fixed - but not before the people behind famous accounts were revealed and shared on public forums such as 4chan. Almost immediately 'word' spread and a patch was created which shut down the exposure. Welcome to the Brave New World of information dissemination, folks. See here for the article.
So, when you post a reply that is seen as "mean" (although it is merely truthful) you are replying to her dad....or to some Indian guy....or to.....??? Hiding behind the skirts of a little girl. That is what terrorists do when they use human shields,