So fiction showing people were thinking about X at such and so a time not evidence people were thinking about X at such and so a time???

All the "get to the moon" or beyond SF, which per Robert Heinlein was an explicit goal of his juveniles, to teach the attitudes and what you needed to learn to to get into space, which he was later told actually worked for a number of Apollo project people was ... what??

Can't make fusion reactors that interesting and the SF series never tried except when they didn't get a chance to shut down properly and went boom (actually a very beginning plot point), but I'm glad for all the fiction creators who inspired me into a STEM career when I was young.

I believe pfdietz's point is there's no need to go to the Moon (or Jupiter?!) to extract 3He when sufficient 3He can be generated on Earth, at lower cost, and be energy positive.

Your digression seems irrelevant to that point.

We didn't use Heinlein stories as a source of evidence about reality. We didn't use thorium rockets to get to the Moon. Nor did we develop monoatomic hydrogen ("Single-H") fuel.

Similarly, we don't use Gundam stories.

Also, Project Daedalus' proposal to mine the Jupiter atmosphere for 3He for fusion predates the first Gundam episode, and is likely what influenced the series. https://en.wikipedia.org/wiki/Project_Daedalus .

If we're going to mine someplace in the solar system for 3He, I'd like to see it done on a (currently hypothetical) "Planet X", a Mars to Earth sized planet 100+ AU from the Sun. It could be cold enough out there for a bit of helium to remain bound over the life of the solar system, but it would be much easier to take off from again than, say, Uranus. And presumably with D3He fusion one could get out there with a fusion rocket.