I read the first post you'd linked to after I commented, rather dimly, and it did make me reel a bit, because I don't actually think my desire to pull off a narrative effect trumps a reader's need not to be further traumatised. I guess it's not been massively difficult for me thus far because I've never written, in fic, anything commonly triggery and if I did, as I say, I think I would warn - but ... I have written triggery things in plays, and I've thought about it quite a lot. There's no system for warning in plays beyond reviews, and I wonder if an expanded review system with quite generalised warnings wouldn't be a better compromise for fic - but impossible, I guess, to sustain. I don't know. I do get the argument about fic's having a different audience to mainstream media and it doesn't hurt me to post warnings. Uncommon triggers though, I don't think anyone can be expected to legislate for. A warning for everything would simply be posting the entire story without a cut. And there stories that, if you were to warn for character death, you may as well not write the story. Basically I think it's a courtesy but not an obligation.

(And I've never done age specifications. I think those are pretty arbitrary and baffling to apply.)