It's not so much slavery but feudalism. It is a return to form. I think there are a lot more people capable of self-actualization and meaning in the dune universe than our own.
>We're as readers meant to take the extremist "correct" position that of course labor is its own virtue and that therefore automating anything is wrong.
I don't think the book forces the reader to take a position on anything. It just portrays a brutal yet intricate medieval-like society.
It is only sci-fi and not fantasy in the sense that some people are concious of their role as both a cause and effect of ecology. (Whereas in our modern society we are only the cause, and in our ancient history we are only an effect).
The reason why everyone's hands are tied is because they are constrained by politics/war/religion/culture/economics/technology and if you tug the thread back the it all goes back to ecology. The key mover in the plot isn't paul but pardot kynes.
Edit:
Shower thought. There is a fifth element in dune that is able to free people from their political/religious/cultural/economic constraints. It's love. People do irrational things out of love. Paul Atredies was a forbidden love child, and his existence is the impetus for the whole conflict and his existence as a messiah destroys pardot kynes' post-mortem plan.