> prince Fëanor

> one of the good guys

Uhhhh...

Feanor drew his sword on his half-brother and threatened to kill him because he was paranoid Fingolfin was trying to usurp his power. He compelled all of his sons to swear an oath to slay any man, elf or being in possession of the silmarils (which led to subsequent needless bloodshed).

Then he ordered and carried out the mass-murder of relatively unarmed Teleri in order to rob them of their ships.

Such actions does not a good guy make.

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.