Destruction

[-Imrahil-]

The three "craftsmen" you mentioned Aulë, Saruman, and Sauron strayed from the path of light. Aulë not so much, and Sauron had already pledged allegience to Melkor because of his greed. But Saruman, Saruman was the one who had good intentions perhaps at first, but as JenFramp said was corrupted by his greed for the invention and creation of things of power. He created things in his own, weaker way (in mockery of Sauron).

I also thing JenFramp has a great point about technology. Tolkien saw it as a destructive force that was changing this world, in his view, for the worse. And indeed, look at this world now, while it is true technology has helped this world and it's people in many ways it is also true that it is destroying it, and soon, if we aren't careful, will destroy it. Technology is the cause of great things, but it also causes horrible things. Tolkien is trying to get at the horrible things it does, when he shows Saruman's work on the Shire.