alt Hacker NewsThere is quite a bit of literature about the Palantir and the related philosophy, whether thy were allegories, etc.
AFAICT the consensus is that they are a very catholic concept and an illustration of what could happen when you use the weapon of your enemy and in general don’t understand the means you use to your end and how even strong people deceive themselves willingly when they think they act for the greater good (movie Denethor is a fool but book Denethor is wise and shrewd, but misguided by despair and Sauron’s manipulation).
So yes, strictly speaking the palantirs are neutral. But that’s missing the whole point of the story.
To me it’s completely fitting. They want to use Evil’s tools but they are Denethor, not Aragorn (who did not over-estimate his will and knew not to get too close). They think that what is good for them is good for the world, and it completely warped their perception.
I'm not familiar with the literature and consensus on them being a Catholic concept, but I am sure they are not about using the enemy's weapon, at least in the sense that you're arguing.
They were created by the high elves and given to the kings of Númenor. The only rightful uses of them in LoTR is by Denethor and Aragorn.
I suppose it could be argued that the illegitimate use of them by Sauron and arguably also Saruman eventually factors in their downfall, and as such it is their use of the enemy's weapons which is fraught--in Saruman's case, that he gets corrupted (but I interpret him already vain and arrogant, and thus on a downward path even before).
In Sauron's case I think lies a nugget of what wisdom Tolkien hoped to confer, especially in his interaction with Pippin. The palantír invites speculation, in that it lets you see things but not all things. Sauron knows a little (the ring is with a Hobbit), is shown a little (here is a Hobbit in Saruman's stone) and in speculating draws wrong conclusions (this is the Hobbit I've been looking for!, etc).
His seeing Aragorn in the stone is different in that Aragorn is the rightful heir, has authority over the stones, and shows truth with intent, which scares Sauron, sends him in a panic and drives him to make foolish decisions.
So, while we are told about the danger of using the enemy's weapon, I'd argue it's from the opposite perspective, and also not quite whatever moral or other lesson Tolkien hoped to confer, rather I believe the moral of the story is to avoid speculation about what happens in another place, or time, and instead trust in yourself, follow your heart and do what is good.