I agree with the first bit - saying that an appeasement strategy against the Horde would have worked or that it would even be the duty of the alliance to not fight back is just a valid interpretation of the lore, the themes of the story or the historic paralels that the horde invasions borrow from.
But the second bit, I have a problem with.
Internment camps as a permanent solution are always wrong and the lore very much portrays them as such. They are not prisons where specific war criminals are being imprisoned, they are camps where the entire people of the horde, men, women and children, are being held against their will while having to do slave labor and there is no exit strategy, except for some Alliance members pushing for genocide. Portraying them as some sort of necessary and just punishment instead of the Gulags that they are is ethically wrong and not supported by the story at all.
I'm not saying that the Alliance should just have given them a piece of land and left them alone - they didnt really know about the whole demon blood thing and there was no indication that that wouldnt have just let to the next attemp to wipe out humandkind, but that doesnt make their solution a just one.
(caveat: I am aware that this is a game and I am not actually outraged
)