Inherent Evil

[Nils]

Since the orcs were corrupted elves in the beginning, and if elves were considered to have a soul(were they?), then orcs would still have a soul.

I agree with Sharku when he said:

let me add that while the notion of orcs being corrupted Elves may have been the idea at the time of Tolkien's writing of LotR, later theories should be given more importance here.

From what I've seen, Morgoth could not destroy anything that had been created, neither could he create.

If you are talking about Souls, then this is true.

From Morgoth's Ring pg 218

Now the Eldar are immortal within Arda according to their right nature. But if a fea (or spirit) indwells in and coheres with a hrondo [>hroa] (or bodily form) that is not of its own choice but ordained, and is made of the flesh or substance of Arda itself, then the fortune of this union must be vulnerable by the evils that do hurt to Arda, even if that union be by nature and purpose permanent. For in spite of this union, which is of such a kind that according to unmarred nature no living person incarnate may be without a fea, nor without a hrondo [>hroa], though the fea cannot be broken or disintegrated by any violence from without, the hrondo [>hroa] can be hurt and may be utterly destroyed.

Because of the inherent evil in the soul, every race has the potential for evil.

Evil is not inherent to the soul, it is inherent to the body.

From Morgoth's Ring pg 399-400

Melkor ‘incarnated’ himself (as Morgoth) permanently. He did this so as the control the hroa, and ‘flesh’ or physical matter, of Arda. He attempted to identify himself with it. A vaster, and more perilous, procedure, though of similar sort to the operations of Sauron with the Rings. Thus, outside the Blessed Realm, all ’matter’ was likely to have a ’Melkor ingredient’, and those who had bodies, nourish by the hroa of Arda, had as it were a tendency, small or great, toward Melkor: they were none of them wholly free of him in their incarnate from, and their bodies had an effect upon their spirits.