Is it the author's opinion that the creation of house elves was a terribly evil deed? It would seem that to think that after their creation, they would want to do what they have been designed to do and so would be no more evil than creating an intelligence which would want to bowl and fish all day. Even if we accept that creating conscious entities which are forced by means of their preferences to do menial work is wrong, it would seem to be better to create them, than to force those who don't enjoy such work to do it. Is Harry just confused by his intuitions about the evil of slavery, without sufficient reflection?

ETA: While this argument works in the abstract and is useful for countering human biases against "slavery" and applies in the particular for the creation of Gammas, Deltas and Epsilons, house elves have addition features I wasn't considering which makes their creation morally evil.