[Feanaro]

That often used quote proves nothing, and the quotes directly before it say that it proves nothing! Here is the entire passage as seen in The Silmarillion

"But of those unhappy ones who were ensnared by Melkor little is known of a certainty. For who of the living has descended into the pits of Utumno, or has explored the darkness of the counsels of Melkor? Yet this is held true by the wise of Eressëa, that all those Quendi who came into the hands of Melkor, ere Utumno was broken, were put there into prison, and by slow arts of cruelty were corrupted and enslaved; and thus did Melkor breed the hideous race of the Orcs in envy and mockery of the Elves, of whom they were afterwards the bitterest foes."

I have the liberty of boldfacing all particular points of interest. This quote is nothing more than a theory devised by the wise elves of the Tol Eressëa. Whether the elves got it right or not remains to be seen.