Presuming said miracle is possible, geoengineering at a scale capable of "solving" climate change would be a massive gamble. Humanity's ability to model the climate simply isn't at a point where we could say with any confidence what the long-term effects of any particular geoengineering "solution" would be, and short of an abrupt technological singularity, won't be for centuries. Without any appeal to moral judgments whatsoever, it's safe to say geoengineering would only be seriously attempted out of total desperation and signal persistent unresolved issues.

If we could solve climate change purely technologically, I wouldn’t feel let down by the fact that we solved climate change. I would absolutely support solving it in that way.

I would also feel frustrated by the knowledge that there were many people who were willing to sacrifice unimaginable numbers of humans and animals for the sake of making more profit for themselves, who were not held to account for their actions. If a person acts in a way that they should know will lead to future suffering, the development of an unforeseen technological solution to that suffering should not wipe their moral slate clean.

Trying to kill someone using a non-functional weapon, that you believe is functional, is not morally equivalent to taking no action just because it didn’t have an effect.

Not unhinged, just human. There's even a logic to their views: when different approaches to a problem are on different sides of a line of political polarization, people see them as competing, and see the success of one as tending to invalidate the other. I've heard/read politically minded people on either end of the spectrum talk about global warming as a challenge that is going to discredit the other side, by which they mean that the success of their preferred approach will discredit other approaches. And I think there's a lot of truth to that, because of how most human beings see things. Thinking from an engineering mindset, we see different ways of solving a problem as complementary rather than mutually exclusive, and to us it's common sense to 1) pursue both of them simultaneously given the high stakes and uncertainty of success, and 2) continue to improve our understanding of different approaches so we can apply them all effectively in the future in situations that call for them. But thinking from an engineering mindset is not normal. That's not how most people see things. I think the way most people see things could be described as a zero-sum competition for mindshare.

You can even see the tendency to see complementary approaches as competing at work in smaller divisions between people who are mostly politically aligned. For example, when one group wants to take immediate direct action to ameliorate a problem and another group wants to focus on longer-term fundamental solutions, they might fight bitterly and badmouth each other's approaches if they feel they are competing for a finite pool of resources such as funding, political backing, or public attention.

For a more concrete example, think of how the issues facing Black Americans recently came to the forefront of public consciousness, books like Between the World and Me and Stamped from the Beginning were shaping the public conversation, and in this context, some people tried to harness that energy to get the public interested in social class as well. When they tried to inject class into the conversation, they often encountered pushback from people who were like, "Hey, the way the public is paying attention to the Black American experience is really special and amazing right now. Let's focus on maintaining this momentum. Save class consciousness for another day." It's not that the majority of people on the left disagreed about class being an important perspective for gaining insight. They simply believed that the public's appetite to learn about a topic like racism was limited and fragile, and it would collapse faster if they tried to add another topic on top.

For a small minority of deeply ideological people, the feeling of competition was stark and intense. Some claimed that talk about class was an attempt to change the topic away from racism and put white people back in charge, and others claimed that identity politics was a class warfare weapon of distraction. But even people who valued both race and class as ways of understanding society perceived a competition for public attention.