>If an author can't even get that part of science right, why should anyone care what they have to say on another part of science?

That does happen - an author will be educated in a particular field or have some specific domain expertise, and their work will obviously be correct in that one regard, but the science everywhere else will be kind of ridiculous. An author may put meticulous detail into the command structure and tactics of a military sci-fi setting but still portray concepts in physics, biology, etc. which are outdated or inaccurate, or filtered through the author's own prejudice.

I don't think it's reasonable to expect even a "hard SF" author to be an expert in everything, or to expect all the science in such stories to be rigorous and correct. Remember that the reason positronic brains exist in Asimov's books is that he thought "positronic" sounded cool and futuristic. It's complete and utter technobabble, yet his robot stories are still considered "hard SF" by many.

People just have to accept that even so-called "hard SF" is mostly BS, and enjoy stories for what they are.