Space colonization is not at all about gadgets and rockets and planets
I watched Apollo 11 one arms-length from the B&W TV screen. Grew up on Heinlein. The libertarian screed "Moon is a Harsh Mistress" was my favourite.
But you're right, of course. A weird thing is that Heinlein also did a short-story about "Coventry" where the libertarians could all go to be shut of Big Government - and the place was basically run by its organized crime, crudely feudal, which was the realistic picture for how the prison Moon would actually be in the novel 20 years later. (Never think you've nailed Heinlein's own views; he contained multitudes.)
This isn't the reason to be eye-rolling about planetary colonization, though: you'd never get that far. The technical issues are so large that everybody will give up "colonization" after some eventual Mars-base shows no sign of being anything but a giant money drain.
As Charlie Stross says, call me about space colonization when Antarctica is full.
Not sure space bros have yet grappled with the fact that the most efficient solution to founder effect genetic disorders in their colony would be to import gametes from Earth such that none of the offspring would be genetically theirs (exploring this in my sci fi novel). It ranks high up alongside the near-ubiquitous ignorance of how much radiation sucks without a protective magnetic field and atmosphere. Seen estimates that daily dose on Mars is anywhere from 20-100x that of Earth (approximately same as being on ISS) — you'd have to shield those imported gametes pretty well to survive long term.
I'm really enjoying this, but I'd like to offer a bit of a counterpoint. Until well after 1950 it seemed entirely reasonable to assume that the steady improvement in transport technology since the rise of the steam engine would continue to the point where space travel would be as cheap and easy as air travel has become in reality. For the average person, the breaking of the sound barrier presaged a similar breakthrough with respect to the speed of light (the Einsteinian understanding of why this isn't possible was new, and still not fully established).
And little enough was known about Venus in particular to leave open the possibility that it would have a breathable atmosphere.
Finally, worries about overpopulation, which play a big role in the current rhetoric of space colonization, weren't a big deal until the 1960s.
With all these assumptions, there was no need for a complex rationale for going to other planets - it just seemed like an obvious thing to do. For people who grew up at the time, like me, it took a long while and a fair bit of thinking to get away from this mindset.
Exactly what Ray Brander said in the last two paras. In fact, I was pointed here in response to a Mastodon post where I made the point about Antarctica.