Orcs... were elves?

[Galin]

Men never slew Men?


There are plenty of things that can catch your eye in the history of Men, so in my opinion the argument that you are (seemingly) trying to imply here really doesn't go any further than focusing on one side of the coin. When Tolkien considered that Men were the stock for orcs...

'This view of the origin of the Orcs thus meets with difficulties of chronology. But though Men may take comfort in this, the theory remains nonetheless the most probable. It accords with all that is known of Melkor, and of the nature and behaviour of Orcs - and of Men. Melkor was impotent to produce any living thing, but skilled in the corruption of things that did not proceed from himself, if he could dominate them.'

JRRT, Myths Transformed, Morgoth's Ring