[Zigûr]

I agree. Saruman is definitely the 'dangerous progressive' to Denethor's 'dangerous conservative.' I think what we must remember about Saruman as an imitator of Sauron is that he had not yet gone as far on the path to corruption. Sauron had, once, been 'progressive' too: he was intent on bringing about drastic changes to the world by eliminating all of its disorder and mutability, which came to mean eliminating its propensity for change, along with free will. But once he had, to some extent, achieved that goal through the creation of the One Ring he now became obsessed with maintaining that order and enforcing it on the entirety of Middle-earth.

Sauron wanted to change the world into a shape he desired, and then keep it that way forever. Denethor just wanted the nation he had inherited to never change. Saruman desired progress to be accelerated to some preferable state, but his collapse into stagnation is itself visible as the tale reaches its conclusion. By the end of the Third Age in his bitterness and corruption all he was capable of doing was imposing the same oppressive regime on the Shire. Saruman's mistake, like Sauron's before him, was trying to bring about change ex nihilo, which ultimately left him spent and mired in stagnation.