> once used for Evil, are incredibly difficult to use in any other way.

That’s not true. They were only dangerous to use as long as an insanely powerful immortal demon god had one. If you used a Palantir he would notice and draw your eye toward him. He could then make you see what he wanted you to see, unless you were strong enough to resist. He corrupted Saruman and Denethor merely by talking to them, showing them misleading things, and convincing them that he could not be defeated by any means. Kill Sauron and the Palantiri are safe to use again.

The tools are neutral. It is the users who are good or evil.

It’s the same with the Throne of Amon Hen, fwiw. It’s only dangerous to use because Sauron will notice that you’re using it.