Melkor nor Sauron was at their origin evil, because evil do not exist in a vacuum: evil is a result of intent, action and consequence.
These Dark Lords are only evil because of what they chose to do, they had both repeatdely chances to chose otherwise, but they did not repent or swayed from their paths that intended to impose full control and domination of others, without any respect for anyone else but themselves.
Industrialization is a symptom of the evil, as in, lack of respect for living things, not the reason why they are evil.
Repeatedly (throughout the years this is), the reasonings that are presented, without arguments for why Sauron's rule would be good, but with arguments why (though actually hardly why) we should ignore the facts and apperent terrible and selfish acts commited at hand. That, indeed, is as reasonable as these arguments, if presented to a judge by a defense lawyer;
"Your honour, my client did intentionally murder another man just to get his money. But when he was a five years old he did not care for money. We should not judge him for the murder, therefor."
and
"Your honour, my client did intentionally murder another man just to get his money. But everyone else in the world are not perfectly good. We should not judge him for the murder, therefor."
I do not oppose the theories as part of a fun "What if"-scenario, but honestly, if meant to be taken as a serious alternative, they remain as much founded in Middle-earth as the Smurfs, since and because of they do not care to adress the moral implications of the acts Sauron commited or why he chose to do so. I presume the very topic usually arise from to a modern [healty] scepticism towards the labling of 'good' and 'evil' [I'm of old a semi-relativist, so that's nothing new], but it misses the point that evil is not an entity in itself but the result of an ethic.
Tolkien to not present these labels out of the blue, to have an 'easy story', but they are founded in a moral concern for what is done, why is it done and what are the consequences? Without an actual moral debate in favour of an alternative ethics (such as arguments for why everyones freedom should rightfully be subjected to anothers will no matter what, or why life has no value comapired to the subjective will of a Dark Lord, or even for that nothing at all have any value) it has no actual weight to it.
Oh yes, Tolkien is certainly vauge and unclear on many, many topics, but do not confuse lack of knowledge for lack of answers.
Tolkien was very clear on that Orcs reproduced just like the Children [Elves and Men; and Dwarves, if considered his adopted Children] a.k.a mommy daddy baby, and they could and would have intercouse with humans to breed:
There must have been orc-women. But in stories that seldom if ever see the Orcs except as soldiers of armies in the service of the evil lords we naturally would not learn much about their lives. Not much was known.
- letter to Mrs Mundby, 21st Octber 1963
For the Orcs had life and multiplied after the manner of the Children of Ilúvatar; and naught that had life of its own, nor the semblance of life, could ever Melkor make since his rebellion in the Ainulindalë before the Beginning: so say the wise.
- Silmarillion; Of the Coming of the Elves and the Captivity of Melkor
(also in/from HoME 10; Grey Annals)
Finally, there is a cogent point, though horrible to relate. It became clear in time that undoubted Men could under the domination of Morgoth or his agents in a few generations be reduced almost to the Orc-level of mind and habits; and then they would or could be made to mate with Orcs, producing new breeds, often larger and more cunning.
There is no doubt that long afterwards, in the Third Age, Saruman rediscovered this, or learned of it in lore, and in his lust for mastery committed this, his wickedest deed: the interbreeding of Orcs and Men...
- HoME 10; Myths Transformed; X; Orcs
etc.