Take my favorite hard sci-fi writer Greg Egan:
First, he made almost all major characters women. He doesn't know how to write female characters mind you, so they still act like men, swashbuckling across the universe, beating up other men when needed, and having no feminine traits to speak up. Just a "she" label slapped on a man. Oh, is that a major male character? Surprise - he's actually transgender. No, there's no plot reason for it and it will never come up again, the characters just needed an opportunity to brag about how tolerant they are.
But the worst offense is the ignorance of economics. Look, it's a modern, industrial human society without the concept of money! Look at how superior it is to this other society that's still barbarian enough to use money. How do they allocate resources? They just produce stuff because other people need it, man. It's, like cause they love each other, man. 169 million people killed by socialism in the 20th century, and they just didn't know they, like, needed to love each other more, man!
It's OK to write a society that somehow doesn't have money. But ignorance of the socialist calculation debate demonstrates the utter failure of the economics profession to teach the very basics of how an economy works.
Why does politics turn geniuses into babbling idiots?