Is it just me, or does the narrative (whether that's Tolkien or Tolkien "through" Pengolodh) seem to almost trivialize the First Kinslaying? That's not the most accurate word, because it is portrayed as this act of uniquely horrific violence, the consequences of which reverberate throughout the Ages.
But I feel like the story after that simply doesn't treat the Kinslaying seriously beyond how it affects the Noldor, i.e. the Doom of Mandos. Manwe cries for the fall of Feanor, not the murder of the Teleri. The burning of the ships focuses on "treason of kin unto kin." The Helcaraxe is posited as atonement (even by Thingol). Throughout the book, the narrative/or inserts little opinions and judgments of the characters, but takes no issue with Finrod remaining friends with the Feanorians. The Arafinweans forgiving the Kinslaying and concealing the truth from the Sindar is portrayed as a good thing, as seen in the quote below:
"But being true, and wisehearted, and thinking all griefs now forgiven, he spoke no word concerning the kinslaying, nor of the manner of the exile of the Noldor and the oath of Fëanor."
And then we have the Book of Lost Tales, Part 1, which is not canon, but it is relevant because I'm discussing Tolkien's biases here (again, not the most fitting word, but my vocabulary is severely limited these days). In 'The Hiding of Valinor', after the Kinslaying, the Teleri (then called the Solosimpi) demand that Valinor be fenced against the Noldor. At various points, Manwe, Ulmo, and the narrative/or accuse them of listening to and spreading Morgoth's lies.
All of which is to say, I believe that the fandom's tendency to minimize the atrocity of the First Kinslaying is a reflection of the narrative itself. I will complicate my own argument by putting forth the possibility that Tolkien did this deliberately, specifically for Finrod, who got knocked out by "having all his worst hypocrisies flung in his face in six-eight time", as written in this brilliant fic.
But I wrote this at 1am so it could be a cold ass take, I don't know.
