GRRM is the one to blame for the deaths of Rhaenyra's first sons because the Greens are not characters. (Spoilers Extended)

The Greens are just plot devices to cause the deaths of Rhaenyra's children. The Greens are personalityless whose actions have no consequences other than causing the deaths of Rhaenyra's family. The Greens are not villains because they have no personality other than plot devices. GRRM is the one to blame for the deaths of Rhaenyra's first sons because the Greens are not villains.