Orcs... were elves?

[Boromir88]

Manwe, interesting post, there's one little thing though:

or deny the trustworthiness of Treebeard’s memory.~Manwe

That itself is not a difficult thing to do. You pointed out Letter 153, and this Letter specifically points out when Treebeard talks about Trolls being a mockery of Ents.

Also, notice in the quote Treebeard says nothing about Orcs originating from Elves. The line is "in mockery of Ents, as Orcs were of Elves", which says nothing about Orcs originating from Elves, just they were made in mockery of the Elves.

You point out using Treebeard's "great memory," but I don't see how that holds any grounds. Treebeard can remember events from long ago but as Tolkien specifically points out with him there is a lot he didn't understand. When Treebeard talks about Trolls being mockery of Ents as Orcs are to Elves, this has nothing to do with his memory it's what he thinks about Trolls to Ents and Orcs to Elves. And Tolkien specifically talks about Treebeard to show that what his characters say is not always what he feels or what is "correct."

There is a time problem, but Tolkien clearly felt like the Mannish Origin is the most likely and he altered the chronology to try to best fit this theory. When it comes all down to it, it's just what you want to believe. Tolkien liked the Mannish Origin the best, but that doesn't mean the reader has to.