I started to compose a reply to your comment, and it turned out to be a deceptively hard question to answer. My attempt at a succinct answer is that carbon sho

I started to compose a reply to your comment, and it turned out to be a deceptively hard question to answer. My attempt at a succinct answer is that carbon should be more expensive, and that Boeing very likely moved too aggressively to meet the market with a more fuel efficient plane. In some ways – based on my probably naive understanding – consumer desire for a cheaper flight results in increased fuel efficiency, since the cost of flying is heavily dependent on the cost of fuel. Environmentally speaking, that's good. However, better fuel efficiency resulting in cheaper flights leads to people flying more. That's bad. Pricing carbon to reflect its true environmental cost could fix that issue, by raising the price floor. Consumer choice would still drive higher efficiency, but ideally the overall higher cost of carbon would keep flying to a 'sustainable' rate. (Whatever that turns out to be.) What I don't have a clear sense of is whether point-to-point travel with planes like the Max are better for the environment. Theoretically, hub-and-spoke travel is more fuel efficient. The reality ends up being more complicated, with airlines flying half-empty 747s. From what I understand, that makes airlines like Southwest (which operates point-to-point) more fuel efficient. But I'd love to hear a more clear explanation from someone who better understands the subject.