Charles Stross explains why so many Baby Boomer SF writers fall so far short when they write in imitation of Robert Heinlein:
Robert A. Heinlein at the 1976 World Science Fiction Convention
Via Wikimedia Commons.
RAH was, for better or worse, one of the dominant figures of American SF between roughly 1945 and 1990 (he died in 1988 but the publishing pipeline drips very slowly). During his extended career (he first began publishing short fiction in the mid-1930s) he moved through a number of distinct phases. One that’s particularly notable is the period from 1946 onwards when, with Scribners, he began publishing what today would be categorized as middle-grade SF novels (but were then more specifically boys adventure stories or childrens fiction): books such as Rocket Ship Galileo, Space Cadet, Red Planet, and Have Space Suit, Will Travel. There were in all roughly a dozen of these books published from 1947 to 1958, and as critic John Clute notes, they included some of the very best juvenile SF ever written (certainly at that point), and were free of many of the flaws that affected Heinlein’s later works — they maintained a strong narrative drive, were relatively free from his tendency to lecture the reader (which could become overwhelming in his later adult novels), and were well-structured as stories.
But most importantly, these were the go-to reading matter for the baby boom generation, kids born from 1945 onwards. It used to be said, somewhat snidely, that “the golden age of SF is 12”; if you were an American boy (or girl) born in 1945 you’d have turned 12 in 1957, just in time to read Time for the Stars or Citizen of the Galaxy. And you might well have begun publishing your own SF novels in the mid-1970s — if your name was Spider Robinson, or John Varley, or Gregory Benford, for example.
Then a disturbing pattern begins to show up.
The pattern: a white male author, born in the Boomer generation (1945-1964), with some or all of the P7 traits (Pale Patriarchal Protestant Plutocratic Penis-People of Power) returns to the reading of their childhood and decides that what the Youth of Today need is more of the same. Only Famous Dead Guy is Dead and no longer around to write more of the good stuff. Whereupon they endeavour to copy Famous Dead Guy’s methods but pay rather less attention to Famous Dead Guy’s twisty mind-set. The result (and the cause of James’s sinking feeling) is frequently an unironic pastiche that propagandizes an inherently conservative perception of Heinlein’s value-set.
It should be noted that Charles Stross is politically left, so calling something “conservative” is intended to be understood as a pejorative connotation, not merely descriptive.
But here’s the thing: as often as not, when you pick up a Heinlein tribute novel by a male boomer author, you’re getting a classic example of the second artist effect.
Heinlein, when he wasn’t cranking out 50K word short tie-in novels for the Boy Scouts of America, was actually trying to write about topics for which he (as a straight white male Californian who grew up from 1907-1930) had no developed vocabulary because such things simply weren’t talked about in Polite Society. 
Unlike most of his peers, he at least tried to look outside the box he grew up in. (A naturist and member of the Free Love movement in the 1920s, he hung out with Thelemites back when they were beyond the pale, and was considered too politically subversive to be called up for active duty in the US Navy during WW2.) But when he tried to look too far outside his zone of enculturation, Heinlein often got things horribly wrong. Writing before second-wave feminism (never mind third- or fourth-), he ended up producing Podkayne of Mars. 
Trying to examine the systemic racism of mid-20th century US society without being plugged into the internal dialog of the civil rights movement resulted in the execrable Farnham’s Freehold. But at least he was trying to engage, unlike many of his contemporaries (the cohort of authors fostered by John W. Campbell, SF editor extraordinaire and all-around horrible bigot). And sometimes he nailed his targets: The Moon is a Harsh Mistress as an attack on colonialism, for example (alas, it has mostly been claimed by the libertarian right), Starship Troopers with its slyly embedded messages that racial integration is the future and women are allowed to be starship captains (think how subversive this was in the mid-to-late 1950s when he was writing it).
In contrast, Heinlein’s boomer fans rarely seemed to notice that Heinlein was all about the inadmissible thought experiment, so their homages frequently came out as flat whitebread 1950s adventure yarns with blunt edges and not even the remotest whiff of edgy introspection, of consideration of the possibility that in the future things might be different (even if Heinlein’s version of diversity ultimately faltered and fell short).
