Trying to be a bird
But is it truly "always wrong and unjust"?But the problem isn't restricted to Heinlein. It's science fiction authors trying to solve a problem that's already solved. Non universal franchise will always be wrong and unjust and contribute to unequal societies. Instead it shows some less flattering sides of the author. Like David Webers hang ups with a social security net.
Like, the usual point of Heinlein's work is what Charlie Stross calls the 'inadmissable thought experiment', and what lot of Heinlein imitators miss when they write totally uninspired whitebread science fiction that would seem novel to a white cishet man of the 1950s. He's far from the only one, mind you, consider Ian M. Banks' Culture novels. While the Culture takes a nominally democratic form of governance, the artificial intelligence "Minds" that run Culture habitats and ships are so amazingly advanced they can frequently rig the opinion of citizens as they like. They are mostly moral enough to not do this... mostly. Yet, one of the key, foundational assumptions of the Culture is the Minds truly are benevolent, nearly godlike AIs that really do want the best for the people in their care, and are smart enough to actually pick the thing that is best for them, most of the time. The net result is a fully automated luxury space communism with very few restrictions on personal liberties, at least in Banks' view.
The dilemma of democracy is most people have not the faintest clue how to run a country (or they think they do, and they often think very wrongly). So you have them pick representatives who, presumably, can spend time learning how. Except those representatives often spend more time figuring out how to get elected and siphon off a bit of wealth for themselves in the process. The dilemma of autocracy is while it is almost certainly true there exists a human who is truly wiser than everyone else, how do we find them, and how do we keep people who aren't wise but do like power from killing our wise person and taking their throne at first opportunity?
Heck, it's not even the only thought experiment Heinlein tried - and the governmental systems of the Lunar Republic, of the universes that heed Their Wisdom, and the balkanized United States of Friday are wildly different from each other, and from the Terran Federation of Starship Troopers. It only looks like some Ayn Rand-style screed in isolation. But I linked the Stross blogpost because there is something else very true about Heinlein. As a cishet white dude writing about it in the beginning and middle of the 20th century, he tried to look outside the box he grew up in but lacked the vocabulary and often got things wrong. He can look quite silly now, looking back, when he did. But when he got it right, he got it right.