I haven't read the whole thing, I haven't even read the most recent posts, but here's my humble opinion on Merrill and the whole Dalish thing there.
It is my personal belief that people are more than free to choose their own way in life. But they must also accept the consequences of their own actions. Merrill is perfectly responsible for herself. Pol was responsible for his own actions. Merethari was responsible for hers.
Now, playing as a Dalish or asking the storyteller in Origins what the Dalish do, I believe the Dalish have a three-fold mission. The entire point of being a Dalish is to do this.
1. Seek out and recover aspects of elven culture and artifacts. They wander throughout the world, always on the lookout to restore their lost culture, their lost technology, regain their immortality. Eluvians are an ancient elvish artifact that Tevinter was only able to turn into fancy telephones.
2. Seek out a land to call their own. A home.
3. Teach the city elves the old ways, as they had forgotten.
With those three aspects of the Dalish mission, it's obvious the Dalish are all about rebuilding their empire, or at least rebuilding their lost culture.
Now let's look at the eluvians as we see them in the game. Three total. The first we see is in the Dalish origin. Duncan confirms that it is tainted by the darkspawn. He calls it a Tevinter artifact and destroys it to try and contain the taint. But as a Grey Warden, I would hardly call him an expert of ancient elvish technologies, but he is an expert on the taint. Merrill and Merethari are both interested in studying it, but Merethari backs out on it because she too afraid of the darkspawn and the taint itself. She wants nothing to do with it. Merrill feels that if they can learn to understand the mirror, they can find Tamlen again. Originally it has nothing to do with glory or rebuilding the lost legacy, but helping out her clan.
She takes a shard and contains it somehow as they travel North to Kirkwall.
The second eluvian we come across is the one Morrigan activates. Morrigan calls it a portal beyond the realm of men, beyond the Fade. She sent her son through it already, trusting him to be safe. She stole a Dalish book that taught her everything she needed to know about the eluvians (which is ironic because the Dalish themselves couldn't read it, having forgotten the elven tongue and script.) Morrigan admits that it wasn't easy to activate the mirror. She and my Warden disappear into it
The third eluvian we come across is the one Merrill is building from scratch. She isn't repairing the one Duncan destroyed, that's still in Ferelden, tainting elves who come across it. All Merrill has is a shard. Gaider confirmed that Merrill extrapolated information from the shard, researched elvish lore on eluvians extensively, and started building her own based entirely on her research. Merrill admits that if she had lyrium (which the Chantry has a monopoly on the trade) she could have cleansed the shard without blood magic. If Merethari helped her, together they could probably have done it.
But at this point, Merethari absolutely refuses to have anything to do with eluvians, blaming the mirror itself for the loss of two hunters, and fears that Merrill will bring back the taint itself. She even tells the entire clan this tale. Never mind that Merrill cleansed the shard, stayed in close proximity to it, and no one was tainted. Proof that she succeeded.
Merethari also told the entire clan that Merrill was a blood mage. Now Pol is a city elf and was raised in an Andrastian society. His views on blood magic skews his common sense. He was more afraid of Merrill, who would only make frowny faces at him than he was of the Varterral, and ran to his death. But Pol still chose for himself to run towards danger. Merrill had nothing to do with it. All she did was say hi.
Before I move onto act 3 and the destruction of the entire clan, I would like to focus on the short story before the game, and the demon itself. Merrill and Merethari both can hear the demon when they first arrive on Sundermount. It's influencing them, speaking directly to their heads, and they both recognize it. So they investigate. And it becomes stronger the closer they get to the demon. They find the demon trapped outside the Fade (and significantly weaker than he would be otherwise) and sealed within the buddha statue. Merethari says that the demon is perfectly harmless within the statue and they leave.
Merrill returns to the demon later, having no access to lyrium and Merethari refusing to help with anything to do with the eluvians (and Merethari's unamplified magic was able to combat the taint in the Dalish Warden, at least temporarily.) Without lyrium or aid, Merrill asks the demon to teach her blood magic, which he does. She uses blood magic to amplify her own power and cleanses the shard entirely, and the taint, which is what Merethari fears, is now no longer an issue. Merrill leaves and the demon is still trapped.
Now the demon influences people based on their proximity. The short story makes that very clear. So when Merrill went to Kirkwall, she literally had no contact with the demon anymore. Everything she did from that point was on her own. She did her own research, studied the shard, and started building a new eluvian from scratch...probably making her the world's greatest authority on eluvians, with Morrigan probably being one of the only people who can activate them (Finn might be able to do it.)
Merethari, however, still is on Sundermount, and is still being influenced by the demon. She is in closer proximity than Merrill is. And she refuses to touch anything related to the eluvians. She says their ancestors would probably want them buried away (as if she would know that,) and talks about how the mirror cost them two of their hunters. And it wasn't even the mirror itself that did that, but the darkspawn taint. That's no longer an issue.
I don't deny that Merrill had a lot of pride. There's a reason she trumps everyone in the Fade when it comes to the Pride demon (although I think the Pride demon is mind controlling her as they are in the Fade where demons are most powerful....and everyone gets mind controlled except Justice, who is a Spirit.) But Merethari was also incredibly prideful as well. Her status as Keeper and her power as a mage would give Audacity everything he would want from a mage. Add in her ability to free him. Based on power and proximity, Merethari is the most likely target of the demon over the course of seven years.
Now onto the Eluvians themselves. We know they are ancient elven artifacts (point one in the mission of the Dalish). We know Tevinter wasn't able to get what Morrigan did out of them. All they had was communication devices. But imagine this, if every clan had an eluvian, Merethari and the Dalish could have contacted another clan within hours of losing their halla and receive aid and leave within a year, based on the distance of the other clan. It would solve a lot of the problems the Dalish on Sundermount faced. If a clan discovers something big, instead of waiting every ten years when they meet, all the clans could know about it within a day. Same thing if the Dalish found a home. The potential benefits are enormous.
The biggest problem in the game, at least from my perspective, is that Hawke is forced into making a decision to support Merrill or stop her from placing herself in unnecessary danger without knowing all the facts. Hawke has no idea what it means to be Dalish. He has no real clue what an eluvian actually does, So we the players need to form our own opinions based on our own interpretations at this point.
Now I'm going to do a quick synopsis on the integrity and characters of Merrill and Merethari. All in one quest. The hunt for the Varterral. Merrill comes to the clan, and invoked a Dalish rite to get access to the tool (can't remember the name off the top of my head.) Merethari agrees to give it to Merrill in exchange for slaying the Varterral. Hawke and Merrill fulfill their end of the bargain, running into Pol and potentially gathering the amulets of the three dead hunters and returning them. Merethari immediately gives it to Hawke and tells Hawke not to give it to Merrill. The deal wasn't with Hawke, but with Merrill. In addition, Merethari admits to telling the clan that Merrill was bringing back the darkspawn taint, despite not being near them for three years, left of her own volition, and cleansed the shard.
Merethari tried to break the bargain. Merrill upheld her end of it.
Now onto Act 3 and the death of the clan. Like I said at the beginning of this wall of text, everyone is an individual capable of thinking for themselves, but must accept the consequences of their actions. Merethari chose to tell the clan that Merrill was a blood mage (true) and that she would bring back the taint (false), and then invited Merrill to return after the entire clan now hates her (audacious and ridiculous.) Merethari refused to touch any lore or research anything regarding eluvians, feeling the whole thing was cursed and tainted, so she actually knows less than Hawke does about eluvians at this stage in the game. Hawke at least knows they were used as communication devices by Tevinter. Merrill did her research, exercised every route she could think of to building the eluvian and activating it. And when all avenues were taken and found to be dead ends, Merrill knew going to the demon was the literal last option. So she makes arrangements with Hawke and friends to accompany her to Sundermount. She tells an aggressive Hawke that only a very powerful spell could free the demon, and she has no intention of doing that.
And should the worst come to pass anyway, Hawke would kill Merrill. Merrill made preparations to the best of her ability, and even had a fail-safe should things go amiss.
Now at this point, the player can either tell Merethari what we're doing or ignore her. If we tell Merethari, she races up Sundermount ahead of us, and frees the demon. If we do not, then Merethari couldn't have beaten us up there and was an abomination all along.
Abomination-Merethari comes along and tells us that the demon would use the Eluvian to free itself and possess Merrill that way (and I admit that it is feasible that the demon would try and play Merrill, and trick her into connecting the Eluvian to the statue and not to the place Morrigan went) but I seriously question this statement made by her.
For one thing, why on earth...er, Thedas, should I trust someone who refused to look into eluvians all these years? And at this point, the demon could simply be trying to mess with Merrill's head. Merethari knew squat about eluvians. She wanted nothing to do with them. Merrill had built one up from scratch, and only needed to learn how to activate it.
Would she have succeeded, would the demon come through? Would she have a telephone? A portal to meet Morrigan? We'll never know at this point. Thanks to Merethari. We the players simply cannot say what would've happened. There's no way to find out. Merethari unleashed the demon without backup, thereby putting the entire clan and Kirkwall in danger. Refused to listen that the taint was no longer a threat, and was in close proximity to the demon for a decade, being influenced constantly, as shown in the short story.
Granted, Merrill's tunnel vision and pride kept her from listening to other people warning her about the dangers of the eluvian and the demon, but she took precautions. She had contingency plans and a decade of research to support her.
So, Merethari, as an adult, is full accountable for her own actions. She chose to free the demon. She may have fought the demon and was forcibly possessed, she may have allowed the demon to possess her to keep it from helping Merrill, but she went on her own, and paid the price for it. Merrill is not responsible for that.
As for the clan's deaths, should Hawke tell the truth, that's on their heads as well. They fired the first arrow, and struck the first blow. Merrill was mourning and they didn't care. And even if you take accountability for it and let them live, if you return with Merrill, they still attack on sight. They want Merrill dead. Their anger and hate, possibly influenced by the demon as well as Merethari telling them that Merrill was dangerous, and their pride, kept them from seeking the truth for themselves. It was entirely their choice to attack. Merrill didn't attack them, they attacked her.
And they can pay the price for their own choices.
After all,
Hawke: I think I left my pointy-ears and self-righteousness at home.
Hunter: You....Shemlen!
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Merrill: They will destroy themselves, and be too self-righteous to accept help or change their course.(or something like that.)