Good point. Tolkien was well aware of the power persuasive rethorics and dialectics have on people. Sauruman's voice is the voice of a politician (though not nessesarily a lefty
) and a demagog. There were a few of them around for Tolkien to witness during his lifetime too, wasn't there?
Sauron, during his days as handsome Annatar, was quite a slick talker too.
The argument between Turin and Gwildor in Nargothrong regarding their war tactics is another good example of what you speak of. The main reason why Turin won the argument was his delivery, good looks and charisma, not the wisdom behind his words.