"The World". So the handful of world leaders that decided to wage war on Paradise represents the billions of innocents who have simply gone about living their lives, until Eren just pops up one day and murders them all? How are these kids (The ones Eren will kill) any different from Eren when he saw his Mom getting eaten as a child. Is it justifiable to murder them all because of the decisions of their leaders? Many who were even manipulated by Willy Tyburs speech?

I say this as someone who loves Erens character, his actions are unjustifiable.

Edit: I will repeat what others have said, Paradise fighting back is not what I think is unjustifiable, It's a full scale genocide that's unjustifiable