I’m all in favor of megaprojects. Hell, some years ago I made a pretty good stab at a book on the subject… half history of such projects, half illustrated manual of such projects, and half manifesto calling for mankind to plow ahead with such projects. Things like solar power satellites, O’Neill habitats, supra-mundane terraforming, orbital rings, terraformed asteroids (inside and out), Dyson swarms, all that. If mankind is going to make it long-term, we are going to have to do such things, and do rather a lot of them. We will eventually tear apart whole solar systems to rebuild them better. And to get from Here to There, we are going to have to do a lot of intermediate projects… and a lot of them will fail. I suspect that a fair proportion of the early space habitats will turn into disasters; early Mars colonies will be death traps; solar power satellites will fold up like origami. It’s sad, but it’s likely inevitable. It’s not like the history of Europeans colonizing the world was a history of unalloyed success from the get-go; there are whole colonies that just up and friggen’ vanished. But humans learn from such things and do better the next time… and soon enough, the same people who vanished like a fart in the wind at Roanoke have built New York City.
That said: not all megaprojects sound like good ideas. Some that seem like they are probably technically feasible sound like logistic or sociological nightmares. Such is the case with The Line, a whackadoo concept for a skyscraper taller than the Empire State Building… and hundreds of kilometers long. Worse, they want to build the thing in the desert. Worst, they want to build it in *Arabia.* No matter how bad your idea is, building it in a backwards theocratic superstitious cesspit will make your idea even worse.