Well, the blatant sexism might be a starting point...
Heinlein's vision of the future was really good for red-blooded males in space suits.
The females got proverbially bashed over the head with a club and dragged-off to a cave - and, they purported to enjoy the process and be witty and intelligent, while dressing scantily and behaving provocatively.
Hell, most of our "heroes" are flawed. Larry Niven advocated bestiality - for aliens, but then so did Alfred Bester and Tolkien...