They didn't.
Where you and he differ is in your judgment of how likely fusion programs are to succeed.
I personally don't think ITER is worth pursuing. I'm skeptical about other tokamak efforts as well. Small efforts that might yield more attractive reactors (Zap, Helion) may be worth pursuing, not least because such efforts would be cheaper.
magnetic confinement, lasers, material sciences have all advanced because of these projects and had impacts in other markets.
even if the money invested never ends up with an ITER reactor. we've still come out ahead economically.
without the original research, the spinoffs may never occur because the initial capital outlay isn't warranted for the various individual uses.
the fact of the matter is fusion reactors are such a game changer ignoring them because of the chance they might not work is insane. meanwhile all the research into getting them to work generates a ton of economic activity because other smaller markets can take advantage of the technological progress that was made in the attempt.
Claims that space spending had a 8:1 (or 24:1, or whatever) payback via spinoffs have typically just assumed the spending has the same macroeconomic payoff of private R&D spending, which demonstrates absolutely nothing.
Without that contribution inflation, one has to somehow show that a particular technology would not exist without the putative spinoff contribution. And that's really difficult to do in most cases. Here, the military has had an interest in high power millimeter wave sources for a variety of reasons.
The argument remains, also, that if spinoffs are an inherent part of research, then it doesn't matter what the research is on, and so you get the highest payoff by funding research that makes sense via direct benefits, as the spinoffs come regardless. You'd need to argue that fusion is somehow better at producing spinoffs than other research. I find that likely; I suspect small scale research is more likely to provide spinoffs, as desktop technologies seem likely to have more applications.
you can hand wave 'possible alternative realities' all you want but the fact is they triggered those economic returns. spacex would be another (recent) example of a primarily NASA funded endeavor that will generate massive returns in the future and would not exist without said funding.
anyways good luck.
> the fact is they triggered those economic returns.
Your blind faith in this dogma is touching, but it isn't supported by real evidence. For example, if you examine what actually happened, the NASA role in developing integrated circuits was rather minor.
Whatever "economic activity" happens around fusion would be overwhelmingly better devoted to building out solar, wind, and storage, to slow the fast developing climate disruption catastrophe.