When Wren says to Haniwa "Vision destroyed the world once", it strikes a blow to the viewers' minds. But the makers or dialogue-writers must have been following their own secret beliefs why saying so because in the series, it was a virus that killed the population and not the vision. In fact, lack of vision has later destroyed the world as people cannot do all that that they were capable of doing with vision. Thus, it seems the makers might have been influenced by several fantasy apocalyptic movies/ series to believe that humans are harmful to the planet and peace. And even if the vision had destroyed the earlier world, the way series is developing doesn't give any faith that their current lack of vision is working to establish any better world. They are barbarians.