I haven't said this but... The reason Octavia was a villain is... Their just very vengeful since they like nature, and due to some destroying nature left them with hatred and revenge, they destroy humanity by either transforming them or killing them off
NOTE : you can be spared by Octavia if they have a bit on mercy on her
NOTE 2 : Even though Octavia likes nature, somehow nature lovers got disintegrated by them due to hatred and the will to destroy humanity clouding their mind