Is it that Sci-Fi is “bad for design”, or when Sci-Fi is poorly designed?

I don’t see any of the examples you listed as “bad FOR design”. They may have had impact to design discourse that were distractions, or led us in directions that were impractical or otherwise not good. But that is different than saying these things were “bad for design”.

In fact I would state the opposite. They teach us things in the speculative setting against stories that would not have otherwise had a space to happen. I would argue that all the bad designs you discuss above were GOOD for design. Yes, there are poor examples of design that still persist, but we keep learning as we keep exploring and learning.

But what is really missing is that we look to Sci-Fi far too strongly for design cues. Sci-Fi is first and foremost about stories and in visual media the interfaces that are expressed are for the purpose of serving the story. They are not meant to be real. They have never been explored in the context of a wider robust researched designed project. They can be inspirational and they can inspire both good and bad ideas.