Another interesting point to think about is the Ents. They are a bit of a mixed barrel when it comes to this debate. They have spent centuries, nay, millennia, wandering their forest, tending the trees, singing their long songs, and all along they had this power. This terrifying power that, ultimately, overthrew Saruman.
I've always admired Gandalf's approach and I agree whole heartedly with your theory, Legate. It was one thing that always nagged me about the way Gandalf was portrayed in the films. Throughout the book we find Gandalf as one unwilling to submit to the enemy in any way; this includes resorting to the enemy's way of doing things. Using his power to fight Saruman would make him no better than the forces he was trying to bring down.
The Ring is the ultimate example of this, I suppose. It is mentioned (I think it's in the Council of Elrond) that if one used the Ring to conquer Sauron, then that one would set him/her self up as a Dark Lord in his place. Galadriel's "in place of a Dark Lord" speech springs to mind. Among the many things the Ring can represent, the use of power to conquer, coerce and control is one of them, I think. Therefore, Gandalf refuses it. He knows that is not the way.
Coming back to the Ents (sorry, I got side tracked), they seem to be strange. They
do use their strength and power to defeat Saruman. You may argue that they had every right to; he had destroyed their trees and used them to fuel his war machines. This is, I think, the point. The Ents could be seen as Saruman's greed coming to bite him in the behind. He uses the trees to further his power, and ultimately, it is those very tools, as it were, that come to bring him down.
I am also reminded of Gandalf's discussion with Denethor about The Ring. When the steward reveals his mind (or some of it) to Gandalf, regarding The One, the Wizard replies "I don't trust you". Knowing that the Ring's power is to destroy and to conquer, he does not trust anyone with it. Not even Himself.
It's rather a lot like the passage in The Bible where, upon being arrested, Jesus tells one of his disciples that he could call down legions of Angels to aid him, but he doesn’t.
Real power, as it were, is not about forcing and conquering.
Gandalf, speaking to Treebeard, seems to support his actions by suggesting that he 'doesn’t want to fill all the world with trees'. I find this interesting. It implies to me that The Ents were not defeating Saruman as much as putting a stop to his actions. Hence, he is not killed by them. They don't even attempt it. That's not what they're there to do.
To paraphrase Gandalf, it's foolish to deal out death and judgement; not even the very wise can see all ends. That's Sauron's way; death, destruction, conquest, the imposing of a will. Gandalf speaks for a way of peace and none violence. I happen to like that.
