Do orcs deserve mercy?

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A post by Troels sparked a thought to explain the fact that orcs are never offered a chance to surrender nor taken prisoner by the 'goodies' in the Lord of the Rings, but instead never surrender and are always slaughtered.

http://parmarkenta.blogspot.com/2011/02/lord-of-rings-as-transitionary-work.html

He relates this to the evolution of the idea of orcs as originating as demons and ending-up as ruined elves or men.

On the concept of orcs as ruined free folk, they should always be offered a chance to 'repent' and be taken prisoner - in a post-LotR letter Tolkien says that orcs never in fact take this chance, since they are so indoctrinated that they believe they would be horribly tormented by their enemies.

This sounds a bit unlikely; humans that are orclike are terrified of dying, often cowardly and inclined to surrender and hope for the best.

BUT if orcs are indeed demons - and as demons are 'fallen angels', then orc-demons are (according to the theology I have read - and in this respect unlike humans) incapable of repentance; therefore deserve no mercy - or, at least mercy, would be futile.

And this could explain why orcs seem never to surrender (despite being cowardly) and never are (at least not that we see) offered mercy or taken prisoner by elves, men or dwarves.

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