I agree that enslaved programmers would probably make worse software, and make it slower, than not-enslaved programmers. Perhaps this is one reason why programmers are not commonly kidnapped and enslaved, or why people who have been kidnapped and enslaved are not usually then compelled to write software. (I can think of others.)

But I'm not sure how this is relevant. We already know that the world of Viliam's thought experiment is not the real world, and it shouldn't be a surprise that there are reasons why it isn't. We can still ask "what would and should happen if somehow it were?".

If you're suggesting that Viliam's hypothetical world is so ridiculous -- because obviously slaves would make rotten programmers -- that there's no point asking that question, though, I can't agree. I don't think it's any more obvious that slaves would make rotten programmers than that slaves would make rotten prostitutes, and for quite similar reasons. Sex, like programming, doesn't work best under conditions of extreme stress.