The educated guess for the last 50 years was 20-30 years away

My wife showed me once a chart of both founding and the estimation of the fusion spark (plus net energy). It explained pretty good why the estimation had changed.

My impression is that if humanity had focused on the question and not the politics we would already have fusion capacity.

But do not forget, we still do not know if it is financial benefit to use fusion in the future.

For the last 60 years even! Fusion power was ~20 years away in Stanislaw Lems Summa Technologicae in 1961.

This is mostly because it has not been funded to the level required for that timeline to be accurate.

https://upload.wikimedia.org/wikipedia/commons/a/ab/U.S._his...

Funding at the level in that chart would not have given us fusion. That chart is based on a crash program to develop tokamaks, but assumed tokamaks work better than they actually do. The main product of that crash program would have been tears and frustration, not practical fusion.

One can turn this around and say that fusion not getting the funding in that chart is evidence it was not seen as a promising place to invest. One cannot simply presume it's a good investment and ignore any evidence to the contrary.

> But compare it to [perpetual motion or faster-than-light space travel].

That's a completely inaccurate comparison - perpetual motion and faster-than-light violate fundamental physical laws as we understand them. Net-positive power from fusion is fully within the laws of physics – we've got an example in the daytime sky, and trillions in the nighttime sky. The difficulties with fusion come with shrinking it to a scale that humans can build.

I think you misunderstood the GP comment.

I understand the GP comment as saying "First commercial fusion power station construction will start 2050-2060" is different from "Perpetual motion machine construction will start in 2050-2060" or "FTL spaceship construction will start in 2050-2060" for the very reasons you gave (among others).

You read the GP as saying something different from what you are saying, but I think you are actually both saying the same thing.

What fusion does is come close to ignoring the laws of engineering and economics. That's not quite the same as ignoring the laws of physics, but either of those is capable of rendering a technology a nonstarter.

Specifically, for fundamental reasons DT fusion will have much lower power density than a fission reactor, and so have to be much larger, and therefore have to be much more expensive.

I would compare it to a space elevator (for earth, not the moon). Do you think we can attach a timeline to that?