I personally think he was just troubled and was not in the right state of mind, after all he went through many events that made him bitter to his very end:
- The death of his mother Miriel
- His Father taking up another wife and having kids with her
- Having a rivalry with Fingolfin
- His father being murdered by Morgoth
- Morgoth stealing his silmarils and hauling @$$ to Beleriand
Yes caused a kinslaying of elves and burned their ships but I don't think he was thinking clearly as to what he did. Death and jealousy can make anyone act rash and foolhardy at times and I think Fëanor was suffering from elvish PTSD and was just hellbent on seeking revenge for his father's death ( seriously who wouldn't want to avenge their parent's murder) and the thievery of his jewels that he crafted from the two trees of Valinor.