[Anguirel]

...the hallowed Silmaril tolerated him, and filled him with its light. Had he been as War Bringer describes, the Silmaril would have burnt him as it burnt poor Maedhros and Maglor.

The death of Feanor's father sent him fey, far more so even than usual. Fey characters in literature and history are doomed, incapable of actions that are not two-edged in their destruction. Had Feanor reacted in a saner way, and been able to calm down, he would not, as others have said, have been Feanor.