The plot centers around artificial flesh and bone life (the robots) which "lack nothing but a soul" used as a forced labor class with outcomes you might imagine.
Given the origin, really "robots, not slaves!" doesn't hold up as a particularly strong argument.
Edit: The related word Robotnik (like the villain in Sonic) means something like "serf" though
This is unequivocally false. I speak both Czech ans Slovak, with the word robota being Czech in origin. Robota either means work in general, or manual labour specifically. It does not, nor has it ever, meant slavery. The word for that would be otroctvo in Slovak or otroctví in Czech.
There isn't really any ambiguity to it and I have never seen the word used as some sort of analogy or synonym for slavery (certainly not in common parlance, though I'm sure it has been used that way somewhere, sometime). If someone wishes to talk about slavery, they will use the appropriate word.