And yet even Feanor was a “good guy” at one point in time. It wasn’t until many years after the invention of the palantiri that he went off the rails, and that was only after talking to Sauron for a while.

But I think that Feanor’s character is irrelevant. An evil person could create a tool that ends up being useful for good purposes. Tools are neutral; they don’t inherit the character of their creator or their user.