There have been past illusions (easy, we now know they are) about going to space.
The canon (Jules Verne)...
The one stage (atomic) rocket to the Moon and back (Hergé (Tintin) and countless others).
The Moonbase as a Post Apollo Program.
The O'Neill L5 space colonies......
The Shuttle was supposed to be extremely safe, launch 50 times a years, divide by so much the costs of sending things and humans to space, help build a space station, and spaceships and solar space power, start a microgravity material processing industry....
None of it happened and 2 orbiters are lost killing their crews because there was no escaping possibility.

The Shuttle turned out indeed to be re-usable but many other things that were supposed to happen around the shuttle program, did not, and the whole idea of re-usability is now mostly buried.

Now, we have illusions about the Moon and Mars.

Ok, yes, the Moon won't be the place where Oxygen can be extracted and where a moonbase can be built and become cost-effective.
But even digging a hole inside the Moon and putting a Transhab inside it, recover it , will greatly help with the human presence on the Moon and the temperature and radiation problems (1 meter below the surface, the temperature is the same whether it's night or day on the surface and there's protection against solar radiation and cosmic rays).
There is science from the Moon (even if the public doesn't care), but there is a spectacular show too and the public should love it at least for a little while even if the human presence is only temporary.

And selling Mars as the only place where In Situ Resources Utilization can take place...Long before any actual test on Mars has taken place....Isn't it also contributing to the illusion? We didn't know about all the 0G processing limitations until we started to work on them.
Let's suppose ISRU is workable , there is still the serious issue of the time to get there, to stay there and return back from there, under a shower of solar radiations.

ISRU is a way to sell Mars, but there are other aspects of a manned Mars program that are very difficult to master or undertand until we test them incrementally.

Raoul