It’s not that fossil fuels themselves are moral. They are energy dense and therefore burning them creates a cheap, reliable source of energy that is needed to transform environments and humans.
Our immune system as well as other important systems like economies and politics are antifragile. They require stressors and challenges in order to learn, adapt, and grow. Systems that are antifragile become rigid, weak, and inefficient when nothing challenges them or pushes them to respond vigorously. Muscles, bones, and children are antifragile.