Hesitated for a bit. Then I thought about the impossibility of Heinlein not thinking about “A Princess of Mars” more then a few times when he wrote it.
Plus a few minutes ago I just read this:
“Isaac Asimov believed that Heinlein made a swing to the right politically at the same time he married Ginny.”
But hey the guy did invent the water bed. A device guaranteed to ruin sex, loving or unloving, for anyone. His frustration would be expected even at his age and health.