While I agree with your points, I am really surprised that you made three such intense posts instead of "it was a valid choice for Fiona, stop harassing her". 
Cute. 
Valid choices for the player =/= characters doing stupid things and refusing to acknowledge their faults.
It's like this:
- if the player was in charge of the mage rebellion and had the option to sell them into slavery, I'd defend that option to the death as a valid player choice. A poor choice, with terrible consequences; but as long as the player is free to make it, and self-aware enough to admit it may have been a mistake when faced with the consequences, still a valid one (see: the Iron Bull outcome in Trespasser). Fiona is an NPC, she's not acting on the rules of roleplaying (eg. there are no rules) - she answers to the writing, and the writing coddles her instead of holding her choices accountable. If the player can be punished for their choices, the NPCs should not get free passes.
- Cullen's lyrium subplot is a choice made by the player, thus it is a roleplaying choice, and I will defend to the death your right to make whatever choice you want here. I may disagree with your choice on a personal level, I may not want to make such a choice on my own game; but as long as a choice is in the game for you to make it, I will defend it as a valid one. This is not the only difficult choice to defend in the series, but to stay on the same example: if Cullen had made the decision to go back on lyrium on his own, as an NPC, with no input from the the player, and say, betrayed the Inquisition, joined the Red Templars etc, I would absolutely hold him, the character, accountable for it (not the player - the player did nothing here). And if Cullen got his ass saved by the Inquisition and said "I did nothing wrong, it was, uhm, I don't know, Samson's fault, he's really convincing" instead of acknowledging his role in it, I would say the writing was coddling him as well.
(Why do I like Samson as a hot mess who cocks up and ruins everything? Because when you catch him, he says "yeah I screwed up, and what of it." He shows his motives, but never blames someone else for his mistakes. Catch me when Fiona the Innocent and Blameless starts owning up to hers.)
So yes, I know my usual spiel is "stop harrassing players for making maybe awful but still valid choices," but Fiona is not a player and I don't have to defend her stupidity. She had the agency to make mistakes, great - now take responsibility and own up to them. You wanna make poor choices on your own game? Shine on, you crazy diamond. You're not an NPC, so you don't answer to writing that affects every player - you answer to the fates of game consequences, and it's not anyone's place to tell you how to play your own game (as it is the writers' place to make their characters, too, accountable for bad decisions, not just the player). Clearer?