Sauron
isevil, no doubt on that. But Sauron is not
absolutely evil. He may be irredeemably evil, at least within the framework of
The Lord of the Rings, but he remains a creature God (in Tolkien's secondary world).
Tolkien does not explain away evil (otherwise he would be the ur-grimdark author!). The existence and persistence of evil is a core theme of his legendarium. However, Tolkien does not explain evil either, or if it attempts an explanation that is done in mythological terms (i.e. Ainulindalë).
Upon rereading LotR two years ago after decades, I was actually surprised to notice how the Dark Lord figure is quite relativized. There are many other evils, in Middle-earth and competing interests, and possibility of Falls that could turn good characters (Boromir, Galadriel, Gandalf) to evil.
What I contest is that you can reduce the Tolkienian treatment of evil to a pure "Us vs. Them" dichotomy, or reducing evil in his work as a pure matter of perspective. It has be done, notably in a few rewritings, but you end up with something rather different from LotR at its kernel.
Sorry, maybe I am murking things even more. I guess you're right, it would require a way longer discussion to conclude that Bakker is wrong. I have to give up on Orcs, the matter is really convoluted and there would be too much to write. On one hand they are born of hate, but on the other Tolkien stated and restated that "the Shadow cannot make only mock". I add two quotes on their nature, that could help to further the discussion.
From Letter 153, Tolkien's Letters
[Eru/God] gave special 'sub-creative' powers to certain of His highest created beings: that is a guarantee that what they devised and made should be given the reality of Creation. Of course within limits, and of course subject to certain commands or prohibitions. But if they 'fell', as the Diabolus Morgoth did, and started making things 'for himself, to be their Lord', these would then 'be', even if Morgoth broke the supreme ban against making other 'rational' creatures like Elves or Men. They would at least 'be' real physical realities in the physical world, however evil they might prove, even 'mocking' the Children of God. They would be Morgoth's greatest Sins, abuses of his highest privilege, and would be creatures begotten of Sin, and naturally bad. (I nearly wrote 'irredeemably bad'; but that would be going too far. Because by accepting or tolerating their making — necessary to their actual existence — even Orcs would become part of the World, which is God's and ultimately good.) But whether they could have 'souls' or 'spirits' seems a different question; and since in my myth at any rate I do not conceive of the making of souls or spirits, things of an equal order if not an equal power to the Valar, as a possible 'delegation', I have represented at least the Orcs as pre-existing real beings on whom the Dark Lord has exerted the fullness of his power in remodelling and corrupting them, not making them.
And this, about how to deal with them according to the "Wise" (Myths Transformed, section VIII, in Morgoth's Ring):
But even before this wickedness of Morgoth was suspected the Wise in the Elder Days taught always that the Orcs were not 'made' by Melkor, and therefore were not in their origin evil. They might have become irredeemable (at least by Elves and Men), but they remained within the Law. That is, that though of necessity, being the fingers of the hand of Morgoth, they must be fought with the utmost severity, they must not be dealt with in their own terms of cruelty or treachery. Captives must not be tormented, not even to discover information for the defence of the homes of Elves and Men. If any Orcs surrendered and asked for mercy, they must be granted it, even at a cost.* This was the teaching of the Wise, though in the horror of the War it was not always heeded.
Tolkien wrote a lot of controversial statements on the origin and the nature of Orcs, and he could not find a proper solution that fit with his worldview. So there is room for ambiguity, but to insofar as to state they are outside the Law (of Eru/God).