[signalToNose]

So it’s mainly a science and engineering challenge that may or maybe not have any practical application. Quite similar to manned space missions and even bigger particle accelerators etc. The diminishing returns on these mega projects will strain the public’s support both financially and politically. James Webb telescope was a huge success. But many other projects have not resulted in much either science or business.

[piva00]

Which is just the nature of exploration in science and engineering, we can't know what lies ahead before exploring a domain... If we could we probably wouldn't need ever to explore anything because we would have discovered how to predict the future.

Or how do you expect pushing the edges of our knowledge to work?

[EvgeniyZh]

All large-scale quantum computers are private; they technically do not need public support. I'd argue that having moonshot projects is a net positive for society, and I'm really happy that Google, for example, invests a non-trivial amount of money in them.