He saw the utter ruin of the Noldor, and as one of the above posts states, he was misinformed. It was a rash act and he could not hope to triumph over Morgoth, but I think his actions were done in the heat of the moment.
Rash and Utterly Heroic !!
Fingolfin is one of my favorite characters. He was a very good king in my opinion, and died like every hero should. Morgoth was greatly wounded during that battle, and I think it helped a lot in the following events.
I agree with you he was misinformed and felt desperate. But, well, he wasn't the wisest elf (it was Finarfin, according to Tolkien), but he was wise enough (maybe the wisest in Beleriand), and when he came to the door of Angband after Feanor's death, he thought it was not the moment to attack, so he rejoined the army and wait patiently for the best moment. Why did he not do the same after the war of the flame and waited to search and rejoin the army? Because, ok, he thought everything was lost, his troops were destroyed, but he knew his son's Gondolin was hidden and safe, as Nargothrond, as Doriath... His troops were destroyed, but his sons, Maedhros, were still around... If he only had a mobile at that moment...
A seeing stone might have done better than a cell phone...
I cannot help but respond to this. I would say both. Misinformed and always leading with emotion rather logic. At the Kinslaying he came late, was lied to, and acted out. I think many factors went in his challenge of the Black Thief. The Melkor he saw chained put on a good show for all to see. I think Feanor was the only Elf to see through that and, in my opinion, his insight came from the lust for power he had in his own heart. But when Fingolfin made his challenge, the emotion of thinking his people vanquished along with a skewed view of Morgoth led him to it. The fact that he wounded the Vile One is a testament to how he loved his people and how strong the Noldor were at the beginning of their struggles in Beleriand.