Assuming one created elf like creatures ex nihilo, not as slightly modified versions of a existing species [...]

Why does this matter? Suppose I create house elves based on a template of an existing, sapient, non-servant species. However, I do not use individuals as templates; the new house elf servants I create are as unique as any newborn unmodified elf. I can even create them as newborns and raise them appropriately.

What is wrong about this? How does creating new elves who enjoy being servants switch from Good to Evil due to existence of other, causally unrelated 'wild' elves, assuming I don't harm them?

Note: given what Eliezer has shown of the wizarding world, I don't doubt that whoever created house elves (if anyone did) modified existing grown elves to make the first generation. It seems intuitively simpler somehow when doing things by magic. And of course fits the whole 'accidentally sneezing sapience on a carrot without even THINKING of the moral consequences" theme :-)