...and Gandalf suddenly had a brilliant idea of how to win the war.

[The Saucepan Man]

But Kuruharan is also right in terms of the moral questions this might raise, of whether any means are justified in order to achieve a 'greater good'.

But, to my mind, Tolkien is quite specific on this in no lesser manner than in his formulation of the basic plot to LotR. The Ring could have been used to defeat Sauron (by Gandalf at least, if not by others on the basis of what is said in the Letters). Yet, although the cause would have been the same, Tolkien makes it clear that it would have been wrong for the "West" to have done so. The whole philosophy of LotR is based on the proposition that it is wrong for the West to use the devices of the Enemy to defeat him (and no phantom, I still don't consider the "diversion" at the Black Gate to be akin to a device of the Enemy. )

Of course things are rarely so clear cut in real life, much as we might want them to be ...