I feel differently about this, and I'll explain, but am in no way invalidating anyone's roleplay reasons. I also understand this reasoning for keeping the vallaslin.
However, being a history nerd, one of the things that irks me is the reconstructed ethnic nationalism among peoples who were oppressed and lost touch with their actual heritage. A lot of it is sentimentalism, or just concocted BS, and this colors both the popular consciousness and in the past it also influenced historical scholarship- not in a good way. As archaeology reveals things about assumptions on national and ethnic identities, to my mind, clinging to the sentimental, constructed ethnic identity rather than the factual truth is a false sense of security and can become a political tool to reinforce division rather than anything meaningful.
Likewise I think the Dalish have to grow and change as they learn more about the real truth of their past, and move forward on a different basis, because in all practicality they're fading. They no longer even have a collective identity, and literally are dying out. If they don't change, they won't have any basis on which to move forward. Keep the vallaslin or not, doubling down on what they've been doing is not going to get them anywhere.
So, my view affects my Lavellan's view- also because she's kind of a scientist. You go where the truth leads you. It's an integrity thing, and though I'm sure she'll have conflicted feelings about it especially after Solas leaves her, would still have no regrets.
Dalish: Blood-writing, refusing to submit to human authority, respecting mages as leaders and advisers.
Mine own cousins the French and their Gallic revival: Dem mustaches. 
But yeah, that's a pet peeve of mine as well. (Putting it lightly.)
The fact that, like I imagine most history classes in school do, my American textbooks really emphasized the American myths of history rather than the bare facts upset me and led to a lot of passive-aggressive mockery in my essays.
Then we got to Advanced U.S. history with a teacher who was a very sweet man, that very calmly explained to my astonished classmates just how complicated the past really was. 
I'm trying to think of more examples of this historical reconstruction to enable unity.
Ah.
So, Macedon and Macedonia. Feel free to correct me if I screw something up, because I've only vaguely followed the arguments here.
Macedon (Or Makedon, or Makedonica, or Those Bearded Terrors With Big Sticks Up North). Seen as barbarians by the Greeks for a time, they eventually joined the Great Big Fraternity of Hellenes by virtue of adopting a lot of Greek Culture, conquering Greece, and beating up Achaemenid Iran together. This is how a lot of the legendary Bromances of Antiquity tended to start.
The modern-day Republic of Macedonia. Largely Bulgarian Slavs. Formerly part of Yuogslavia. Their territory is largely the territory of the old Thracian tribes who raided and/or were clients of the Kingdom of Macedon. But they've been in disputes with Greece for years, as Greece has Macedonia as a province, and lots of Macedonian Greeks, and the rest of Ancient Macedon's territory. Particularly, the Macedonians trying to use the Vergina Sun on their flag, one of Macedon's most famous symbols. They've even started building statues of Phillip and Alexander and naming streets and airports after them.
It vexes me. You've got an interesting enough history on your own, guys! You don't need to siphon off Alexander's glory! 
I mean, I understand why people do it, but I still don't like it.
My Lavellan will keep the vallaslin, because goddammit they have seven hundred years of being symbols of their gods. And, slave markings or not, they were the symbols of their gods. And the symbols worn by priest-warriors like Abelas. Since she is bound to Mythal as he is, and her vallaslin are of Mythal, and Mythal is the ****, she keeps them. A new twist on an old concept. The Dalish should learn more about the true history, but there's no need to drop it entirely.
My other Lavellan refused the Well and was disgusted with all of the jackass god revelations and the slavery, and has rejected old Arlathan culture. "Why not build new elven glories, and not on the back of slaves?"
But yeah, the Dalish are not going a good place. They're not united, they're clinging to old memories because that's all they have. They need to do something.
Solas is probably doing something, which isn't really a comfort. 
I like how bold the vallaslin are, though. "This is my face. This is my elfy-elf face. If you don't like my being an elf, try to take me down. I dare you. I've also got this elfy-elf OP spec called Knight-Enchanter Arcane Warrior. Try me, shemlen."