Having robots makes Felix really happy. Not as happy as having slaves, but still happier than anyone else could ever be.
Anyway, well, then, that seems to leave some big question marks. How is everyone who goes through utilitarian moral reasoning supposed to decide between help and neglect, and hope to come up with the same answer? (Because if two people come up with sufficiently different answers, it may lead to one or both concluding that the expected utility of violently enforcing obedience from the other person is worth the cost, unless they have deontological rules of some sort. Like the kind that the article says Mill supported.)
If someone is vegetarian/vegan for ethical reasons, it's because they want there to be fewer factory farms. This would of course mean that the animals they would have eaten wouldn't exist at all, so of course they'd consider nonexistence better than a life of torture.
"I'd rather you not have lived at all, rather than live a life of torture" is a pretty mainstream opinion in general, I think.
Unless cloning counts? Is extinction okay as long as we have some copies of their DNA and plan to clone them into a decent life eventually? I feel rather uneasy about that resolution; at the very least I'd want to see a species successfully reconstructed in this manner before giving the possibility moral weight.