It is easier for me to list the Heinlein books I HAVEN'T read rather than the ones I have... I never fully read SIASL, Friday, Farnham's Freehold, or The cat that walked through walls. I started to read them but never got into them...

Heinlein had an odd world view and he certainly let it show. It wasn't that he couldn't write strong female characters, its just that the only women in his books that were not highly negative female stereotypes were 'HIS TYPE' of woman... Just look at starship troopers, and Moon is a Harsh Mistress. His female characters were either 'his type' or they were silly, shallow, vapid, subhuman creatures put there for annoying background noise. I don't know if you could call this 'sexism' or not since he applied the same sort of 'all or nothing' attitude to his male characters as well.

It may be that he just viewed all people in this black-and-white way. It is a superficial view of humanity that, in my opinion, detracts from a story. As an example of a sci-fi writer that approaches a story from the OPPOSITE viewpoint I would have to cite Orson Scott Card. He does an excellent job of making his characters more than 2-dimensional.