Two quick points re STARSHIP TROOPERS. One, there was only one screenwriter
really, Ed Neumeier, who initially wanted to write a love triangle story
against the background of an alien bug war. This was his impetus, not
adapting Heinlein. He assumed the screen rights to Heinlein's novel had
been taken, but discovered that he was wrong. The rights were purchased,
the title ideal, and some of Heinlein's concepts were injected, but his
main motivation was telling the tale he devised (Rico loving girl and
joining military to be near her only to have her promoted into areas he is
unable to follow).
Two: The most interesting thing about the propaganda breaks is that they
are a fresh, quick, and clever way to rapidly deliver exposition. Instead
of being lectured, the audience is entertained while filled in on important
background information. But as has been pointed out, the satire in these
segments is out of sync with the rest of the film.
And for what it is worth point number three, Heinlein's book is an
entertainment and canny piece of propaganda that would not make an action
movie and is more concerned with how its callow hero learns to become a
soldier and an officer. The majority of the book is taken up with his
training and the lessons that he learns (how to prioritize; how to delegate
or assume authority, etc.) Such a military lesson would probably not
attract or continue to attract a large audience the way Verhoeven's eye
candy has. (At the same time, it is depressing to see a segment of the
audience that wants nothing more from science fiction than big space
battles....)