In your opinion, who does have the most insight into morality?

Game theorists.

can one say "these lives should not have been created" and "these lives are still worth living"?

Yes, but why would one want to?

You once wrote "life on the farm is, for most, horrible". Would you still agree with that?

Yes. I will note that it was in the context of a rural America vs. an industrial America; given that real choice between potential states, I saw far more glory and happiness in the latter than the former.

Does it imply that antinatalism is correct in societies where most people are farmers?

No, because choices should be made in the context of the real alternatives facing the decision-maker. Agricultural lives may be worse suited to the preferences of most people than industrial lives, and industrial lives may be worse suited to the preferences of most people than post-singularity lives, but the choice facing any potential parent in any of those ages is "would I prefer another human related to me in era X, or not?" rather than "what era would I like my child to be born in?"