

But her clan and Keeper are as short sighted as you are, and assume it is impossible, just because a Gray warden that knows less than an apprentice about magic said it, they all assume it is bad, and rain rage and prejudies on Merril who is trying to do what Marethari had the duty to do: KEEP the history.
She did clear the mirror from taint, she did fix it, and she was completely aware of the danger that the demon posed, and she was willing to risk it and take the fall by herself, to help all the elves, all for her people, that is called being a HERO!
But Marethari had to be stupid and let the demon posses her, if it was Merril facing the demon she could kill it when it tryed to escape by the mirror, specially with the help of te champion, but the keeper had to screw it all, and after the keeper suicided the entire clans prejudies got the needed fuel to burst in flames, all Merril did was defend themselves, they all died by their own stupidity.
The mirror was clean, she got secrets and power from the demon, and she was willing to face it by herself and not endanger her clan, but they all made it impossible!!!
I know this is old, but you’re both right and wrong, the two of you. Yes, Merrill was simply trying to restore Dalish history that had been lost to time because of Duncan, but on the other hand, Duncan had to do it because that same eluvian caused Tamlen to become tainted, and he was trying to prevent others from following suit. He was trying to save lives. Noble ideas all around, but flawed in every way. All I think of this is that some secrets are best left forgotten.

The point you brought about the Eluvian being bad is right, it had Darkspawn taint, but then Merril purified it from the taint! Everything else that happened wrong was due to Marethari's and her clan's stupidity. Merril had the skill to remove taint a veteran gray warden could not, and the brillance to actually recover valuable Elven history/magic/culture/power, something that, guess what, is the keeper's job, Marethari only made all worse, Merill is 10 times better keeper.
Don’t get me wrong dude, I know Marethari wasn’t too good to her, but I also understand her caution: loosing another Tamlen was something she wanted to avoid. Besides, I don’t think anyone outside the wardens knows how to “cure” an object. In fact, I don’t know if the wardens themselves know how to completely cure anything that was blighted. You can delay it sure, by destroying those things that were affected or by having someone go through the Joining, such as what happens with the Dalish Warden, but afaik, you can’t truly ”cure” something that’s tainted. If you have proof of the contrary, I’d love to read it.
edit: in other words, Merrill is playing with fire.

Sure, Merrill WAS playing with fire, but the bad consequences were not of her making, everything bad that happened was The Keeper and her clan's fault not hers. And Merril did fix the mirror.
And I know what you are talking about Marethari, she was too fearfull of losing another Daelish to the taint, but that fear made her do stupid stuf, like spread prejudies to her clan, scorning Merrill and made her get possessed by the Pride Demon. That was all on her not on Merrill.
Now the bigger picture here is, the Dalish live like shit, they have to rebuild their culture, and bringing back the Mirror would be a big step on the right direction, Merrill knew there were risks, but she was willing to suffer them for her people, that is the most beautiful thing. She was not wrong, and we could with little effort kill the demon and everything would be alright. but Marethari and her Clan had to make all intu a shitstorm.